src/librustc/middle/stability.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A pass that annotates every item and method with its stability level,
  12 //! propagating default levels lexically from parent to children ast nodes.
  13
  14 pub use self::StabilityLevel::*;
  15
  16 use dep_graph::DepNode;
  17 use hir::map as hir_map;
  18 use lint;
  19 use hir::def::Def;
  20 use hir::def_id::{CrateNum, CRATE_DEF_INDEX, DefId, DefIndex, LOCAL_CRATE};
  21 use ty::{self, TyCtxt};
  22 use middle::privacy::AccessLevels;
  23 use syntax::symbol::Symbol;
  24 use syntax_pos::{Span, DUMMY_SP};
  25 use syntax::ast;
  26 use syntax::ast::{NodeId, Attribute};
  27 use syntax::feature_gate::{GateIssue, emit_feature_err, find_lang_feature_accepted_version};
  28 use syntax::attr::{self, Stability, Deprecation};
  29 use util::nodemap::{DefIdMap, FxHashSet, FxHashMap};
  30
  31 use hir;
  32 use hir::{Item, Generics, StructField, Variant};
  33 use hir::intravisit::{self, Visitor, NestedVisitorMap};
  34
  35 use std::mem::replace;
  36 use std::cmp::Ordering;
  37
  38 #[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Copy, Debug, Eq, Hash)]
  39 pub enum StabilityLevel {
  40     Unstable,
  41     Stable,
  42 }
  43
  44 impl StabilityLevel {
  45     pub fn from_attr_level(level: &attr::StabilityLevel) -> Self {
  46         if level.is_stable() { Stable } else { Unstable }
  47     }
  48 }
  49
  50 #[derive(PartialEq)]
  51 enum AnnotationKind {
  52     // Annotation is required if not inherited from unstable parents
  53     Required,
  54     // Annotation is useless, reject it
  55     Prohibited,
  56     // Annotation itself is useless, but it can be propagated to children
  57     Container,
  58 }
  59
  60 /// An entry in the `depr_map`.
  61 #[derive(Clone)]
  62 pub struct DeprecationEntry {
  63     /// The metadata of the attribute associated with this entry.
  64     pub attr: Deprecation,
  65     /// The def id where the attr was originally attached. `None` for non-local
  66     /// `DefId`'s.
  67     origin: Option<DefIndex>,
  68 }
  69
  70 impl DeprecationEntry {
  71     fn local(attr: Deprecation, id: DefId) -> DeprecationEntry {
  72         assert!(id.is_local());
  73         DeprecationEntry {
  74             attr: attr,
  75             origin: Some(id.index),
  76         }
  77     }
  78
  79     fn external(attr: Deprecation) -> DeprecationEntry {
  80         DeprecationEntry {
  81             attr: attr,
  82             origin: None,
  83         }
  84     }
  85
  86     pub fn same_origin(&self, other: &DeprecationEntry) -> bool {
  87         match (self.origin, other.origin) {
  88             (Some(o1), Some(o2)) => o1 == o2,
  89             _ => false
  90         }
  91     }
  92 }
  93
  94 /// A stability index, giving the stability level for items and methods.
  95 pub struct Index<'tcx> {
  96     /// This is mostly a cache, except the stabilities of local items
  97     /// are filled by the annotator.
  98     stab_map: DefIdMap<Option<&'tcx Stability>>,
  99     depr_map: DefIdMap<Option<DeprecationEntry>>,
 100
 101     /// Maps for each crate whether it is part of the staged API.
 102     staged_api: FxHashMap<CrateNum, bool>,
 103
 104     /// Features enabled for this crate.
 105     active_features: FxHashSet<Symbol>,
 106
 107     /// Features used by this crate. Updated before and during typeck.
 108     used_features: FxHashMap<Symbol, attr::StabilityLevel>
 109 }
 110
 111 // A private tree-walker for producing an Index.
 112 struct Annotator<'a, 'tcx: 'a> {
 113     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 114     index: &'a mut Index<'tcx>,
 115     parent_stab: Option<&'tcx Stability>,
 116     parent_depr: Option<DeprecationEntry>,
 117     in_trait_impl: bool,
 118 }
 119
 120 impl<'a, 'tcx: 'a> Annotator<'a, 'tcx> {
 121     // Determine the stability for a node based on its attributes and inherited
 122     // stability. The stability is recorded in the index and used as the parent.
 123     fn annotate<F>(&mut self, id: NodeId, attrs: &[Attribute],
 124                    item_sp: Span, kind: AnnotationKind, visit_children: F)
 125         where F: FnOnce(&mut Self)
 126     {
 127         if self.index.staged_api[&LOCAL_CRATE] && self.tcx.sess.features.borrow().staged_api {
 128             debug!("annotate(id = {:?}, attrs = {:?})", id, attrs);
 129             if let Some(..) = attr::find_deprecation(self.tcx.sess.diagnostic(), attrs, item_sp) {
 130                 self.tcx.sess.span_err(item_sp, "`#[deprecated]` cannot be used in staged api, \
 131                                                  use `#[rustc_deprecated]` instead");
 132             }
 133             if let Some(mut stab) = attr::find_stability(self.tcx.sess.diagnostic(),
 134                                                          attrs, item_sp) {
 135                 // Error if prohibited, or can't inherit anything from a container
 136                 if kind == AnnotationKind::Prohibited ||
 137                    (kind == AnnotationKind::Container &&
 138                     stab.level.is_stable() &&
 139                     stab.rustc_depr.is_none()) {
 140                     self.tcx.sess.span_err(item_sp, "This stability annotation is useless");
 141                 }
 142
 143                 debug!("annotate: found {:?}", stab);
 144                 // If parent is deprecated and we're not, inherit this by merging
 145                 // deprecated_since and its reason.
 146                 if let Some(parent_stab) = self.parent_stab {
 147                     if parent_stab.rustc_depr.is_some() && stab.rustc_depr.is_none() {
 148                         stab.rustc_depr = parent_stab.rustc_depr.clone()
 149                     }
 150                 }
 151
 152                 let stab = self.tcx.intern_stability(stab);
 153
 154                 // Check if deprecated_since < stable_since. If it is,
 155                 // this is *almost surely* an accident.
 156                 if let (&Some(attr::RustcDeprecation {since: dep_since, ..}),
 157                         &attr::Stable {since: stab_since}) = (&stab.rustc_depr, &stab.level) {
 158                     // Explicit version of iter::order::lt to handle parse errors properly
 159                     for (dep_v, stab_v) in
 160                             dep_since.as_str().split(".").zip(stab_since.as_str().split(".")) {
 161                         if let (Ok(dep_v), Ok(stab_v)) = (dep_v.parse::<u64>(), stab_v.parse()) {
 162                             match dep_v.cmp(&stab_v) {
 163                                 Ordering::Less => {
 164                                     self.tcx.sess.span_err(item_sp, "An API can't be stabilized \
 165                                                                      after it is deprecated");
 166                                     break
 167                                 }
 168                                 Ordering::Equal => continue,
 169                                 Ordering::Greater => break,
 170                             }
 171                         } else {
 172                             // Act like it isn't less because the question is now nonsensical,
 173                             // and this makes us not do anything else interesting.
 174                             self.tcx.sess.span_err(item_sp, "Invalid stability or deprecation \
 175                                                              version found");
 176                             break
 177                         }
 178                     }
 179                 }
 180
 181                 let def_id = self.tcx.hir.local_def_id(id);
 182                 self.index.stab_map.insert(def_id, Some(stab));
 183
 184                 let orig_parent_stab = replace(&mut self.parent_stab, Some(stab));
 185                 visit_children(self);
 186                 self.parent_stab = orig_parent_stab;
 187             } else {
 188                 debug!("annotate: not found, parent = {:?}", self.parent_stab);
 189                 if let Some(stab) = self.parent_stab {
 190                     if stab.level.is_unstable() {
 191                         let def_id = self.tcx.hir.local_def_id(id);
 192                         self.index.stab_map.insert(def_id, Some(stab));
 193                     }
 194                 }
 195                 visit_children(self);
 196             }
 197         } else {
 198             // Emit errors for non-staged-api crates.
 199             for attr in attrs {
 200                 let tag = attr.name();
 201                 if tag == "unstable" || tag == "stable" || tag == "rustc_deprecated" {
 202                     attr::mark_used(attr);
 203                     self.tcx.sess.span_err(attr.span(), "stability attributes may not be used \
 204                                                          outside of the standard library");
 205                 }
 206             }
 207
 208             if let Some(depr) = attr::find_deprecation(self.tcx.sess.diagnostic(), attrs, item_sp) {
 209                 if kind == AnnotationKind::Prohibited {
 210                     self.tcx.sess.span_err(item_sp, "This deprecation annotation is useless");
 211                 }
 212
 213                 // `Deprecation` is just two pointers, no need to intern it
 214                 let def_id = self.tcx.hir.local_def_id(id);
 215                 let depr_entry = Some(DeprecationEntry::local(depr, def_id));
 216                 self.index.depr_map.insert(def_id, depr_entry.clone());
 217
 218                 let orig_parent_depr = replace(&mut self.parent_depr, depr_entry);
 219                 visit_children(self);
 220                 self.parent_depr = orig_parent_depr;
 221             } else if let parent_depr @ Some(_) = self.parent_depr.clone() {
 222                 let def_id = self.tcx.hir.local_def_id(id);
 223                 self.index.depr_map.insert(def_id, parent_depr);
 224                 visit_children(self);
 225             } else {
 226                 visit_children(self);
 227             }
 228         }
 229     }
 230 }
 231
 232 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 233     /// Because stability levels are scoped lexically, we want to walk
 234     /// nested items in the context of the outer item, so enable
 235     /// deep-walking.
 236     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 237         NestedVisitorMap::All(&self.tcx.hir)
 238     }
 239
 240     fn visit_item(&mut self, i: &'tcx Item) {
 241         let orig_in_trait_impl = self.in_trait_impl;
 242         let mut kind = AnnotationKind::Required;
 243         match i.node {
 244             // Inherent impls and foreign modules serve only as containers for other items,
 245             // they don't have their own stability. They still can be annotated as unstable
 246             // and propagate this unstability to children, but this annotation is completely
 247             // optional. They inherit stability from their parents when unannotated.
 248             hir::ItemImpl(.., None, _, _) | hir::ItemForeignMod(..) => {
 249                 self.in_trait_impl = false;
 250                 kind = AnnotationKind::Container;
 251             }
 252             hir::ItemImpl(.., Some(_), _, _) => {
 253                 self.in_trait_impl = true;
 254             }
 255             hir::ItemStruct(ref sd, _) => {
 256                 if !sd.is_struct() {
 257                     self.annotate(sd.id(), &i.attrs, i.span, AnnotationKind::Required, |_| {})
 258                 }
 259             }
 260             _ => {}
 261         }
 262
 263         self.annotate(i.id, &i.attrs, i.span, kind, |v| {
 264             intravisit::walk_item(v, i)
 265         });
 266         self.in_trait_impl = orig_in_trait_impl;
 267     }
 268
 269     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem) {
 270         self.annotate(ti.id, &ti.attrs, ti.span, AnnotationKind::Required, |v| {
 271             intravisit::walk_trait_item(v, ti);
 272         });
 273     }
 274
 275     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem) {
 276         let kind = if self.in_trait_impl {
 277             AnnotationKind::Prohibited
 278         } else {
 279             AnnotationKind::Required
 280         };
 281         self.annotate(ii.id, &ii.attrs, ii.span, kind, |v| {
 282             intravisit::walk_impl_item(v, ii);
 283         });
 284     }
 285
 286     fn visit_variant(&mut self, var: &'tcx Variant, g: &'tcx Generics, item_id: NodeId) {
 287         self.annotate(var.node.data.id(), &var.node.attrs, var.span, AnnotationKind::Required, |v| {
 288             intravisit::walk_variant(v, var, g, item_id);
 289         })
 290     }
 291
 292     fn visit_struct_field(&mut self, s: &'tcx StructField) {
 293         self.annotate(s.id, &s.attrs, s.span, AnnotationKind::Required, |v| {
 294             intravisit::walk_struct_field(v, s);
 295         });
 296     }
 297
 298     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem) {
 299         self.annotate(i.id, &i.attrs, i.span, AnnotationKind::Required, |v| {
 300             intravisit::walk_foreign_item(v, i);
 301         });
 302     }
 303
 304     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef) {
 305         self.annotate(md.id, &md.attrs, md.span, AnnotationKind::Required, |_| {});
 306     }
 307 }
 308
 309 struct MissingStabilityAnnotations<'a, 'tcx: 'a> {
 310     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 311     access_levels: &'a AccessLevels,
 312 }
 313
 314 impl<'a, 'tcx: 'a> MissingStabilityAnnotations<'a, 'tcx> {
 315     fn check_missing_stability(&self, id: NodeId, span: Span) {
 316         let def_id = self.tcx.hir.local_def_id(id);
 317         let is_error = !self.tcx.sess.opts.test &&
 318                         !self.tcx.stability.borrow().stab_map.contains_key(&def_id) &&
 319                         self.access_levels.is_reachable(id);
 320         if is_error {
 321             self.tcx.sess.span_err(span, "This node does not have a stability attribute");
 322         }
 323     }
 324 }
 325
 326 impl<'a, 'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'a, 'tcx> {
 327     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 328         NestedVisitorMap::OnlyBodies(&self.tcx.hir)
 329     }
 330
 331     fn visit_item(&mut self, i: &'tcx Item) {
 332         match i.node {
 333             // Inherent impls and foreign modules serve only as containers for other items,
 334             // they don't have their own stability. They still can be annotated as unstable
 335             // and propagate this unstability to children, but this annotation is completely
 336             // optional. They inherit stability from their parents when unannotated.
 337             hir::ItemImpl(.., None, _, _) | hir::ItemForeignMod(..) => {}
 338
 339             _ => self.check_missing_stability(i.id, i.span)
 340         }
 341
 342         intravisit::walk_item(self, i)
 343     }
 344
 345     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem) {
 346         self.check_missing_stability(ti.id, ti.span);
 347         intravisit::walk_trait_item(self, ti);
 348     }
 349
 350     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem) {
 351         let impl_def_id = self.tcx.hir.local_def_id(self.tcx.hir.get_parent(ii.id));
 352         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 353             self.check_missing_stability(ii.id, ii.span);
 354         }
 355         intravisit::walk_impl_item(self, ii);
 356     }
 357
 358     fn visit_variant(&mut self, var: &'tcx Variant, g: &'tcx Generics, item_id: NodeId) {
 359         self.check_missing_stability(var.node.data.id(), var.span);
 360         intravisit::walk_variant(self, var, g, item_id);
 361     }
 362
 363     fn visit_struct_field(&mut self, s: &'tcx StructField) {
 364         self.check_missing_stability(s.id, s.span);
 365         intravisit::walk_struct_field(self, s);
 366     }
 367
 368     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem) {
 369         self.check_missing_stability(i.id, i.span);
 370         intravisit::walk_foreign_item(self, i);
 371     }
 372
 373     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef) {
 374         self.check_missing_stability(md.id, md.span);
 375     }
 376 }
 377
 378 impl<'a, 'tcx> Index<'tcx> {
 379     /// Construct the stability index for a crate being compiled.
 380     pub fn build(&mut self, tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 381         let ref active_lib_features = tcx.sess.features.borrow().declared_lib_features;
 382
 383         // Put the active features into a map for quick lookup
 384         self.active_features = active_lib_features.iter().map(|&(ref s, _)| s.clone()).collect();
 385
 386         let _task = tcx.dep_graph.in_task(DepNode::StabilityIndex);
 387         let krate = tcx.hir.krate();
 388         let mut annotator = Annotator {
 389             tcx: tcx,
 390             index: self,
 391             parent_stab: None,
 392             parent_depr: None,
 393             in_trait_impl: false,
 394         };
 395         annotator.annotate(ast::CRATE_NODE_ID, &krate.attrs, krate.span, AnnotationKind::Required,
 396                            |v| intravisit::walk_crate(v, krate));
 397     }
 398
 399     pub fn new(hir_map: &hir_map::Map) -> Index<'tcx> {
 400         let _task = hir_map.dep_graph.in_task(DepNode::StabilityIndex);
 401         let krate = hir_map.krate();
 402
 403         let mut is_staged_api = false;
 404         for attr in &krate.attrs {
 405             if attr.name() == "stable" || attr.name() == "unstable" {
 406                 is_staged_api = true;
 407                 break
 408             }
 409         }
 410
 411         let mut staged_api = FxHashMap();
 412         staged_api.insert(LOCAL_CRATE, is_staged_api);
 413         Index {
 414             staged_api: staged_api,
 415             stab_map: DefIdMap(),
 416             depr_map: DefIdMap(),
 417             active_features: FxHashSet(),
 418             used_features: FxHashMap(),
 419         }
 420     }
 421 }
 422
 423 /// Cross-references the feature names of unstable APIs with enabled
 424 /// features and possibly prints errors.
 425 pub fn check_unstable_api_usage<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 426     let mut checker = Checker { tcx: tcx };
 427     tcx.visit_all_item_likes_in_krate(DepNode::StabilityCheck, &mut checker.as_deep_visitor());
 428 }
 429
 430 struct Checker<'a, 'tcx: 'a> {
 431     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 432 }
 433
 434 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 435     // (See issue #38412)
 436     fn skip_stability_check_due_to_privacy(self, def_id: DefId) -> bool {
 437         let visibility = {
 438             // Check if `def_id` is a trait method.
 439             match self.sess.cstore.associated_item(def_id) {
 440                 Some(ty::AssociatedItem { container: ty::TraitContainer(trait_def_id), .. }) => {
 441                     // Trait methods do not declare visibility (even
 442                     // for visibility info in cstore). Use containing
 443                     // trait instead, so methods of pub traits are
 444                     // themselves considered pub.
 445                     self.sess.cstore.visibility(trait_def_id)
 446                 }
 447                 _ => {
 448                     // Otherwise, cstore info works directly.
 449                     self.sess.cstore.visibility(def_id)
 450                 }
 451             }
 452         };
 453
 454         match visibility {
 455             // must check stability for pub items.
 456             ty::Visibility::Public => false,
 457
 458             // these are not visible outside crate; therefore
 459             // stability markers are irrelevant, if even present.
 460             ty::Visibility::Restricted(..) |
 461             ty::Visibility::Invisible => true,
 462         }
 463     }
 464
 465     pub fn check_stability(self, def_id: DefId, id: NodeId, span: Span) {
 466         if self.sess.codemap().span_allows_unstable(span) {
 467             debug!("stability: \
 468                     skipping span={:?} since it is internal", span);
 469             return;
 470         }
 471
 472         let lint_deprecated = |note: Option<Symbol>| {
 473             let msg = if let Some(note) = note {
 474                 format!("use of deprecated item: {}", note)
 475             } else {
 476                 format!("use of deprecated item")
 477             };
 478
 479             self.sess.add_lint(lint::builtin::DEPRECATED, id, span, msg);
 480         };
 481
 482         // Deprecated attributes apply in-crate and cross-crate.
 483         if let Some(depr_entry) = self.lookup_deprecation_entry(def_id) {
 484             let skip = if id == ast::DUMMY_NODE_ID {
 485                 true
 486             } else {
 487                 let parent_def_id = self.hir.local_def_id(self.hir.get_parent(id));
 488                 self.lookup_deprecation_entry(parent_def_id).map_or(false, |parent_depr| {
 489                     parent_depr.same_origin(&depr_entry)
 490                 })
 491             };
 492
 493             if !skip {
 494                 lint_deprecated(depr_entry.attr.note);
 495             }
 496         }
 497
 498         let is_staged_api = *self.stability.borrow_mut().staged_api.entry(def_id.krate)
 499             .or_insert_with(|| self.sess.cstore.is_staged_api(def_id.krate));
 500         if !is_staged_api {
 501             return;
 502         }
 503
 504         let stability = self.lookup_stability(def_id);
 505         debug!("stability: \
 506                 inspecting def_id={:?} span={:?} of stability={:?}", def_id, span, stability);
 507
 508         if let Some(&Stability{rustc_depr: Some(attr::RustcDeprecation { reason, .. }), ..})
 509                 = stability {
 510             if id != ast::DUMMY_NODE_ID {
 511                 lint_deprecated(Some(reason));
 512             }
 513         }
 514
 515         // Only the cross-crate scenario matters when checking unstable APIs
 516         let cross_crate = !def_id.is_local();
 517         if !cross_crate {
 518             return
 519         }
 520
 521         if let Some(&Stability { ref level, ref feature, .. }) = stability {
 522             self.stability.borrow_mut().used_features.insert(feature.clone(), level.clone());
 523         }
 524
 525         // Issue 38412: private items lack stability markers.
 526         if self.skip_stability_check_due_to_privacy(def_id) {
 527             return
 528         }
 529
 530         match stability {
 531             Some(&Stability { level: attr::Unstable {ref reason, issue}, ref feature, .. }) => {
 532                 if !self.stability.borrow().active_features.contains(feature) {
 533                     let msg = match *reason {
 534                         Some(ref r) => format!("use of unstable library feature '{}': {}",
 535                                                &feature.as_str(), &r),
 536                         None => format!("use of unstable library feature '{}'", &feature)
 537                     };
 538                     emit_feature_err(&self.sess.parse_sess, &feature.as_str(), span,
 539                                      GateIssue::Library(Some(issue)), &msg);
 540                 }
 541             }
 542             Some(_) => {
 543                 // Stable APIs are always ok to call and deprecated APIs are
 544                 // handled by the lint emitting logic above.
 545             }
 546             None => {
 547                 span_bug!(span, "encountered unmarked API");
 548             }
 549         }
 550     }
 551 }
 552
 553 impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
 554     /// Because stability levels are scoped lexically, we want to walk
 555     /// nested items in the context of the outer item, so enable
 556     /// deep-walking.
 557     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 558         NestedVisitorMap::OnlyBodies(&self.tcx.hir)
 559     }
 560
 561     fn visit_item(&mut self, item: &'tcx hir::Item) {
 562         match item.node {
 563             hir::ItemExternCrate(_) => {
 564                 // compiler-generated `extern crate` items have a dummy span.
 565                 if item.span == DUMMY_SP { return }
 566
 567                 let cnum = match self.tcx.sess.cstore.extern_mod_stmt_cnum(item.id) {
 568                     Some(cnum) => cnum,
 569                     None => return,
 570                 };
 571                 let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
 572                 self.tcx.check_stability(def_id, item.id, item.span);
 573             }
 574
 575             // For implementations of traits, check the stability of each item
 576             // individually as it's possible to have a stable trait with unstable
 577             // items.
 578             hir::ItemImpl(.., Some(ref t), _, ref impl_item_refs) => {
 579                 if let Def::Trait(trait_did) = t.path.def {
 580                     for impl_item_ref in impl_item_refs {
 581                         let impl_item = self.tcx.hir.impl_item(impl_item_ref.id);
 582                         let trait_item_def_id = self.tcx.associated_items(trait_did)
 583                             .find(|item| item.name == impl_item.name).map(|item| item.def_id);
 584                         if let Some(def_id) = trait_item_def_id {
 585                             // Pass `DUMMY_NODE_ID` to skip deprecation warnings.
 586                             self.tcx.check_stability(def_id, ast::DUMMY_NODE_ID, impl_item.span);
 587                         }
 588                     }
 589                 }
 590             }
 591
 592             _ => (/* pass */)
 593         }
 594         intravisit::walk_item(self, item);
 595     }
 596
 597     fn visit_path(&mut self, path: &'tcx hir::Path, id: ast::NodeId) {
 598         match path.def {
 599             Def::PrimTy(..) | Def::SelfTy(..) | Def::Err => {}
 600             _ => self.tcx.check_stability(path.def.def_id(), id, path.span)
 601         }
 602         intravisit::walk_path(self, path)
 603     }
 604 }
 605
 606 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 607     /// Lookup the stability for a node, loading external crate
 608     /// metadata as necessary.
 609     pub fn lookup_stability(self, id: DefId) -> Option<&'gcx Stability> {
 610         if let Some(st) = self.stability.borrow().stab_map.get(&id) {
 611             return *st;
 612         }
 613
 614         let st = self.lookup_stability_uncached(id);
 615         self.stability.borrow_mut().stab_map.insert(id, st);
 616         st
 617     }
 618
 619     pub fn lookup_deprecation(self, id: DefId) -> Option<Deprecation> {
 620         self.lookup_deprecation_entry(id).map(|depr| depr.attr)
 621     }
 622
 623     pub fn lookup_deprecation_entry(self, id: DefId) -> Option<DeprecationEntry> {
 624         if let Some(depr) = self.stability.borrow().depr_map.get(&id) {
 625             return depr.clone();
 626         }
 627
 628         let depr = self.lookup_deprecation_uncached(id);
 629         self.stability.borrow_mut().depr_map.insert(id, depr.clone());
 630         depr
 631     }
 632
 633     fn lookup_stability_uncached(self, id: DefId) -> Option<&'gcx Stability> {
 634         debug!("lookup(id={:?})", id);
 635         if id.is_local() {
 636             None // The stability cache is filled partially lazily
 637         } else {
 638             self.sess.cstore.stability(id).map(|st| self.intern_stability(st))
 639         }
 640     }
 641
 642     fn lookup_deprecation_uncached(self, id: DefId) -> Option<DeprecationEntry> {
 643         debug!("lookup(id={:?})", id);
 644         if id.is_local() {
 645             None // The stability cache is filled partially lazily
 646         } else {
 647             self.sess.cstore.deprecation(id).map(DeprecationEntry::external)
 648         }
 649     }
 650 }
 651
 652 /// Given the list of enabled features that were not language features (i.e. that
 653 /// were expected to be library features), and the list of features used from
 654 /// libraries, identify activated features that don't exist and error about them.
 655 pub fn check_unused_or_stable_features<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 656                                                  access_levels: &AccessLevels) {
 657     let sess = &tcx.sess;
 658
 659     if tcx.stability.borrow().staged_api[&LOCAL_CRATE] && tcx.sess.features.borrow().staged_api {
 660         let _task = tcx.dep_graph.in_task(DepNode::StabilityIndex);
 661         let krate = tcx.hir.krate();
 662         let mut missing = MissingStabilityAnnotations {
 663             tcx: tcx,
 664             access_levels: access_levels,
 665         };
 666         missing.check_missing_stability(ast::CRATE_NODE_ID, krate.span);
 667         intravisit::walk_crate(&mut missing, krate);
 668         krate.visit_all_item_likes(&mut missing.as_deep_visitor());
 669     }
 670
 671     let ref declared_lib_features = sess.features.borrow().declared_lib_features;
 672     let mut remaining_lib_features: FxHashMap<Symbol, Span>
 673         = declared_lib_features.clone().into_iter().collect();
 674
 675     fn format_stable_since_msg(version: &str) -> String {
 676         format!("this feature has been stable since {}. Attribute no longer needed", version)
 677     }
 678
 679     for &(ref stable_lang_feature, span) in &sess.features.borrow().declared_stable_lang_features {
 680         let version = find_lang_feature_accepted_version(&stable_lang_feature.as_str())
 681             .expect("unexpectedly couldn't find version feature was stabilized");
 682         sess.add_lint(lint::builtin::STABLE_FEATURES,
 683                       ast::CRATE_NODE_ID,
 684                       span,
 685                       format_stable_since_msg(version));
 686     }
 687
 688     let index = tcx.stability.borrow();
 689     for (used_lib_feature, level) in &index.used_features {
 690         match remaining_lib_features.remove(used_lib_feature) {
 691             Some(span) => {
 692                 if let &attr::StabilityLevel::Stable { since: ref version } = level {
 693                     sess.add_lint(lint::builtin::STABLE_FEATURES,
 694                                   ast::CRATE_NODE_ID,
 695                                   span,
 696                                   format_stable_since_msg(&version.as_str()));
 697                 }
 698             }
 699             None => ( /* used but undeclared, handled during the previous ast visit */ )
 700         }
 701     }
 702
 703     for &span in remaining_lib_features.values() {
 704         sess.add_lint(lint::builtin::UNUSED_FEATURES,
 705                       ast::CRATE_NODE_ID,
 706                       span,
 707                       "unused or unknown feature".to_string());
 708     }
 709 }