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 use self::AnnotationKind::*;
  16
  17 use session::Session;
  18 use lint;
  19 use metadata::cstore::LOCAL_CRATE;
  20 use middle::def;
  21 use middle::def_id::{CRATE_DEF_INDEX, DefId};
  22 use middle::ty;
  23 use middle::privacy::PublicItems;
  24 use metadata::csearch;
  25 use syntax::parse::token::InternedString;
  26 use syntax::codemap::{Span, DUMMY_SP};
  27 use syntax::ast;
  28 use syntax::ast::{NodeId, Attribute};
  29 use syntax::feature_gate::{GateIssue, emit_feature_err};
  30 use syntax::attr::{self, Stability, AttrMetaMethods};
  31 use util::nodemap::{DefIdMap, FnvHashSet, FnvHashMap};
  32
  33 use rustc_front::hir;
  34 use rustc_front::hir::{Block, Crate, Item, Generics, StructField, Variant};
  35 use rustc_front::visit::{self, Visitor};
  36
  37 use std::mem::replace;
  38 use std::cmp::Ordering;
  39
  40 #[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Copy, Debug, Eq, Hash)]
  41 pub enum StabilityLevel {
  42     Unstable,
  43     Stable,
  44 }
  45
  46 impl StabilityLevel {
  47     pub fn from_attr_level(level: &attr::StabilityLevel) -> Self {
  48         if level.is_stable() { Stable } else { Unstable }
  49     }
  50 }
  51
  52 #[derive(PartialEq)]
  53 enum AnnotationKind {
  54     // Annotation is required if not inherited from unstable parents
  55     AnnRequired,
  56     // Annotation is useless, reject it
  57     AnnProhibited,
  58     // Annotation itself is useless, but it can be propagated to children
  59     AnnContainer,
  60 }
  61
  62 /// A stability index, giving the stability level for items and methods.
  63 pub struct Index<'tcx> {
  64     /// This is mostly a cache, except the stabilities of local items
  65     /// are filled by the annotator.
  66     map: DefIdMap<Option<&'tcx Stability>>,
  67
  68     /// Maps for each crate whether it is part of the staged API.
  69     staged_api: FnvHashMap<ast::CrateNum, bool>
  70 }
  71
  72 // A private tree-walker for producing an Index.
  73 struct Annotator<'a, 'tcx: 'a> {
  74     tcx: &'a ty::ctxt<'tcx>,
  75     index: &'a mut Index<'tcx>,
  76     parent: Option<&'tcx Stability>,
  77     export_map: &'a PublicItems,
  78     in_trait_impl: bool,
  79     in_enum: bool,
  80 }
  81
  82 impl<'a, 'tcx: 'a> Annotator<'a, 'tcx> {
  83     // Determine the stability for a node based on its attributes and inherited
  84     // stability. The stability is recorded in the index and used as the parent.
  85     fn annotate<F>(&mut self, id: NodeId, attrs: &Vec<Attribute>,
  86                    item_sp: Span, kind: AnnotationKind, visit_children: F)
  87         where F: FnOnce(&mut Annotator)
  88     {
  89         if self.index.staged_api[&LOCAL_CRATE] {
  90             debug!("annotate(id = {:?}, attrs = {:?})", id, attrs);
  91             if let Some(mut stab) = attr::find_stability(self.tcx.sess.diagnostic(),
  92                                                          attrs, item_sp) {
  93                 // Error if prohibited, or can't inherit anything from a container
  94                 if kind == AnnProhibited ||
  95                    kind == AnnContainer && stab.level.is_stable() && stab.depr.is_none() {
  96                     self.tcx.sess.span_err(item_sp, "This stability annotation is useless");
  97                 }
  98
  99                 debug!("annotate: found {:?}", stab);
 100                 // If parent is deprecated and we're not, inherit this by merging
 101                 // deprecated_since and its reason.
 102                 if let Some(parent_stab) = self.parent {
 103                     if parent_stab.depr.is_some() && stab.depr.is_none() {
 104                         stab.depr = parent_stab.depr.clone()
 105                     }
 106                 }
 107
 108                 let stab = self.tcx.intern_stability(stab);
 109
 110                 // Check if deprecated_since < stable_since. If it is,
 111                 // this is *almost surely* an accident.
 112                 if let (&Some(attr::Deprecation {since: ref dep_since, ..}),
 113                         &attr::Stable {since: ref stab_since}) = (&stab.depr, &stab.level) {
 114                     // Explicit version of iter::order::lt to handle parse errors properly
 115                     for (dep_v, stab_v) in dep_since.split(".").zip(stab_since.split(".")) {
 116                         if let (Ok(dep_v), Ok(stab_v)) = (dep_v.parse::<u64>(), stab_v.parse()) {
 117                             match dep_v.cmp(&stab_v) {
 118                                 Ordering::Less => {
 119                                     self.tcx.sess.span_err(item_sp, "An API can't be stabilized \
 120                                                                      after it is deprecated");
 121                                     break
 122                                 }
 123                                 Ordering::Equal => continue,
 124                                 Ordering::Greater => break,
 125                             }
 126                         } else {
 127                             // Act like it isn't less because the question is now nonsensical,
 128                             // and this makes us not do anything else interesting.
 129                             self.tcx.sess.span_err(item_sp, "Invalid stability or deprecation \
 130                                                              version found");
 131                             break
 132                         }
 133                     }
 134                 }
 135
 136                 let def_id = self.tcx.map.local_def_id(id);
 137                 self.index.map.insert(def_id, Some(stab));
 138
 139                 let parent = replace(&mut self.parent, Some(stab));
 140                 visit_children(self);
 141                 self.parent = parent;
 142             } else {
 143                 debug!("annotate: not found, parent = {:?}", self.parent);
 144                 let mut is_error = kind == AnnRequired &&
 145                                    self.export_map.contains(&id) &&
 146                                    !self.tcx.sess.opts.test;
 147                 if let Some(stab) = self.parent {
 148                     if stab.level.is_unstable() {
 149                         let def_id = self.tcx.map.local_def_id(id);
 150                         self.index.map.insert(def_id, Some(stab));
 151                         is_error = false;
 152                     }
 153                 }
 154                 if is_error {
 155                     self.tcx.sess.span_err(item_sp, "This node does not have \
 156                                                      a stability attribute");
 157                 }
 158                 visit_children(self);
 159             }
 160         } else {
 161             // Emit errors for non-staged-api crates.
 162             for attr in attrs {
 163                 let tag = attr.name();
 164                 if tag == "unstable" || tag == "stable" || tag == "deprecated" {
 165                     attr::mark_used(attr);
 166                     self.tcx.sess.span_err(attr.span(), "stability attributes may not be used \
 167                                                          outside of the standard library");
 168                 }
 169             }
 170             visit_children(self);
 171         }
 172     }
 173 }
 174
 175 impl<'a, 'tcx, 'v> Visitor<'v> for Annotator<'a, 'tcx> {
 176     fn visit_item(&mut self, i: &Item) {
 177         let orig_in_trait_impl = self.in_trait_impl;
 178         let orig_in_enum = self.in_enum;
 179         let mut kind = AnnRequired;
 180         match i.node {
 181             // Inherent impls and foreign modules serve only as containers for other items,
 182             // they don't have their own stability. They still can be annotated as unstable
 183             // and propagate this unstability to children, but this annotation is completely
 184             // optional. They inherit stability from their parents when unannotated.
 185             hir::ItemImpl(_, _, _, None, _, _) | hir::ItemForeignMod(..) => {
 186                 self.in_trait_impl = false;
 187                 kind = AnnContainer;
 188             }
 189             hir::ItemImpl(_, _, _, Some(_), _, _) => {
 190                 self.in_trait_impl = true;
 191             }
 192             hir::ItemStruct(ref sd, _) => {
 193                 self.in_enum = false;
 194                 if !sd.is_struct() {
 195                     self.annotate(sd.id(), &i.attrs, i.span, AnnRequired, |_| {})
 196                 }
 197             }
 198             hir::ItemEnum(..) => {
 199                 self.in_enum = true;
 200             }
 201             _ => {}
 202         }
 203
 204         self.annotate(i.id, &i.attrs, i.span, kind, |v| {
 205             visit::walk_item(v, i)
 206         });
 207         self.in_trait_impl = orig_in_trait_impl;
 208         self.in_enum = orig_in_enum;
 209     }
 210
 211     fn visit_trait_item(&mut self, ti: &hir::TraitItem) {
 212         self.annotate(ti.id, &ti.attrs, ti.span, AnnRequired, |v| {
 213             visit::walk_trait_item(v, ti);
 214         });
 215     }
 216
 217     fn visit_impl_item(&mut self, ii: &hir::ImplItem) {
 218         let kind = if self.in_trait_impl { AnnProhibited } else { AnnRequired };
 219         self.annotate(ii.id, &ii.attrs, ii.span, kind, |v| {
 220             visit::walk_impl_item(v, ii);
 221         });
 222     }
 223
 224     fn visit_variant(&mut self, var: &Variant, g: &'v Generics, item_id: NodeId) {
 225         self.annotate(var.node.data.id(), &var.node.attrs, var.span, AnnRequired, |v| {
 226             visit::walk_variant(v, var, g, item_id);
 227         })
 228     }
 229
 230     fn visit_struct_field(&mut self, s: &StructField) {
 231         // FIXME: This is temporary, can't use attributes with tuple variant fields until snapshot
 232         let kind = if self.in_enum && s.node.kind.is_unnamed() {
 233             AnnProhibited
 234         } else {
 235             AnnRequired
 236         };
 237         self.annotate(s.node.id, &s.node.attrs, s.span, kind, |v| {
 238             visit::walk_struct_field(v, s);
 239         });
 240     }
 241
 242     fn visit_foreign_item(&mut self, i: &hir::ForeignItem) {
 243         self.annotate(i.id, &i.attrs, i.span, AnnRequired, |v| {
 244             visit::walk_foreign_item(v, i);
 245         });
 246     }
 247
 248     fn visit_macro_def(&mut self, md: &'v hir::MacroDef) {
 249         if md.imported_from.is_none() {
 250             self.annotate(md.id, &md.attrs, md.span, AnnRequired, |_| {});
 251         }
 252     }
 253 }
 254
 255 impl<'tcx> Index<'tcx> {
 256     /// Construct the stability index for a crate being compiled.
 257     pub fn build(&mut self, tcx: &ty::ctxt<'tcx>, krate: &Crate, export_map: &PublicItems) {
 258         let mut annotator = Annotator {
 259             tcx: tcx,
 260             index: self,
 261             parent: None,
 262             export_map: export_map,
 263             in_trait_impl: false,
 264             in_enum: false,
 265         };
 266         annotator.annotate(ast::CRATE_NODE_ID, &krate.attrs, krate.span, AnnRequired,
 267                            |v| visit::walk_crate(v, krate));
 268     }
 269
 270     pub fn new(krate: &Crate) -> Index {
 271         let mut is_staged_api = false;
 272         for attr in &krate.attrs {
 273             if attr.name() == "staged_api" {
 274                 if let ast::MetaWord(_) = attr.node.value.node {
 275                     attr::mark_used(attr);
 276                     is_staged_api = true;
 277                     break
 278                 }
 279             }
 280         }
 281         let mut staged_api = FnvHashMap();
 282         staged_api.insert(LOCAL_CRATE, is_staged_api);
 283         Index {
 284             staged_api: staged_api,
 285             map: DefIdMap(),
 286         }
 287     }
 288 }
 289
 290 /// Cross-references the feature names of unstable APIs with enabled
 291 /// features and possibly prints errors. Returns a list of all
 292 /// features used.
 293 pub fn check_unstable_api_usage(tcx: &ty::ctxt)
 294                                 -> FnvHashMap<InternedString, StabilityLevel> {
 295     let ref active_lib_features = tcx.sess.features.borrow().declared_lib_features;
 296
 297     // Put the active features into a map for quick lookup
 298     let active_features = active_lib_features.iter().map(|&(ref s, _)| s.clone()).collect();
 299
 300     let mut checker = Checker {
 301         tcx: tcx,
 302         active_features: active_features,
 303         used_features: FnvHashMap(),
 304         in_skip_block: 0,
 305     };
 306
 307     let krate = tcx.map.krate();
 308     visit::walk_crate(&mut checker, krate);
 309
 310     let used_features = checker.used_features;
 311     return used_features;
 312 }
 313
 314 struct Checker<'a, 'tcx: 'a> {
 315     tcx: &'a ty::ctxt<'tcx>,
 316     active_features: FnvHashSet<InternedString>,
 317     used_features: FnvHashMap<InternedString, StabilityLevel>,
 318     // Within a block where feature gate checking can be skipped.
 319     in_skip_block: u32,
 320 }
 321
 322 impl<'a, 'tcx> Checker<'a, 'tcx> {
 323     fn check(&mut self, id: DefId, span: Span, stab: &Option<&Stability>) {
 324         // Only the cross-crate scenario matters when checking unstable APIs
 325         let cross_crate = !id.is_local();
 326         if !cross_crate {
 327             return
 328         }
 329
 330         // We don't need to check for stability - presumably compiler generated code.
 331         if self.in_skip_block > 0 {
 332             return;
 333         }
 334
 335         match *stab {
 336             Some(&Stability { level: attr::Unstable {ref reason, issue}, ref feature, .. }) => {
 337                 self.used_features.insert(feature.clone(), Unstable);
 338
 339                 if !self.active_features.contains(feature) {
 340                     let msg = match *reason {
 341                         Some(ref r) => format!("use of unstable library feature '{}': {}",
 342                                                &feature, &r),
 343                         None => format!("use of unstable library feature '{}'", &feature)
 344                     };
 345                     emit_feature_err(&self.tcx.sess.parse_sess.span_diagnostic,
 346                                       &feature, span, GateIssue::Library(Some(issue)), &msg);
 347                 }
 348             }
 349             Some(&Stability { ref level, ref feature, .. }) => {
 350                 self.used_features.insert(feature.clone(), StabilityLevel::from_attr_level(level));
 351
 352                 // Stable APIs are always ok to call and deprecated APIs are
 353                 // handled by a lint.
 354             }
 355             None => {
 356                 // This is an 'unmarked' API, which should not exist
 357                 // in the standard library.
 358                 if self.tcx.sess.features.borrow().unmarked_api {
 359                     self.tcx.sess.span_warn(span, "use of unmarked library feature");
 360                     self.tcx.sess.span_note(span, "this is either a bug in the library you are \
 361                                                    using or a bug in the compiler - please \
 362                                                    report it in both places");
 363                 } else {
 364                     self.tcx.sess.span_err(span, "use of unmarked library feature");
 365                     self.tcx.sess.span_note(span, "this is either a bug in the library you are \
 366                                                    using or a bug in the compiler - please \
 367                                                    report it in both places");
 368                     self.tcx.sess.span_note(span, "use #![feature(unmarked_api)] in the \
 369                                                    crate attributes to override this");
 370                 }
 371             }
 372         }
 373     }
 374 }
 375
 376 impl<'a, 'v, 'tcx> Visitor<'v> for Checker<'a, 'tcx> {
 377     fn visit_item(&mut self, item: &hir::Item) {
 378         // When compiling with --test we don't enforce stability on the
 379         // compiler-generated test module, demarcated with `DUMMY_SP` plus the
 380         // name `__test`
 381         if item.span == DUMMY_SP && item.name.as_str() == "__test" { return }
 382
 383         check_item(self.tcx, item, true,
 384                    &mut |id, sp, stab| self.check(id, sp, stab));
 385         visit::walk_item(self, item);
 386     }
 387
 388     fn visit_expr(&mut self, ex: &hir::Expr) {
 389         check_expr(self.tcx, ex,
 390                    &mut |id, sp, stab| self.check(id, sp, stab));
 391         visit::walk_expr(self, ex);
 392     }
 393
 394     fn visit_path(&mut self, path: &hir::Path, id: ast::NodeId) {
 395         check_path(self.tcx, path, id,
 396                    &mut |id, sp, stab| self.check(id, sp, stab));
 397         visit::walk_path(self, path)
 398     }
 399
 400     fn visit_path_list_item(&mut self, prefix: &hir::Path, item: &hir::PathListItem) {
 401         check_path_list_item(self.tcx, item,
 402                    &mut |id, sp, stab| self.check(id, sp, stab));
 403         visit::walk_path_list_item(self, prefix, item)
 404     }
 405
 406     fn visit_pat(&mut self, pat: &hir::Pat) {
 407         check_pat(self.tcx, pat,
 408                   &mut |id, sp, stab| self.check(id, sp, stab));
 409         visit::walk_pat(self, pat)
 410     }
 411
 412     fn visit_block(&mut self, b: &hir::Block) {
 413         let old_skip_count = self.in_skip_block;
 414         match b.rules {
 415             hir::BlockCheckMode::PushUnstableBlock => {
 416                 self.in_skip_block += 1;
 417             }
 418             hir::BlockCheckMode::PopUnstableBlock => {
 419                 self.in_skip_block = self.in_skip_block.checked_sub(1).unwrap();
 420             }
 421             _ => {}
 422         }
 423         visit::walk_block(self, b);
 424         self.in_skip_block = old_skip_count;
 425     }
 426 }
 427
 428 /// Helper for discovering nodes to check for stability
 429 pub fn check_item(tcx: &ty::ctxt, item: &hir::Item, warn_about_defns: bool,
 430                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 431     match item.node {
 432         hir::ItemExternCrate(_) => {
 433             // compiler-generated `extern crate` items have a dummy span.
 434             if item.span == DUMMY_SP { return }
 435
 436             let cnum = match tcx.sess.cstore.find_extern_mod_stmt_cnum(item.id) {
 437                 Some(cnum) => cnum,
 438                 None => return,
 439             };
 440             let id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
 441             maybe_do_stability_check(tcx, id, item.span, cb);
 442         }
 443
 444         // For implementations of traits, check the stability of each item
 445         // individually as it's possible to have a stable trait with unstable
 446         // items.
 447         hir::ItemImpl(_, _, _, Some(ref t), _, ref impl_items) => {
 448             let trait_did = tcx.def_map.borrow().get(&t.ref_id).unwrap().def_id();
 449             let trait_items = tcx.trait_items(trait_did);
 450
 451             for impl_item in impl_items {
 452                 let item = trait_items.iter().find(|item| {
 453                     item.name() == impl_item.name
 454                 }).unwrap();
 455                 if warn_about_defns {
 456                     maybe_do_stability_check(tcx, item.def_id(), impl_item.span, cb);
 457                 }
 458             }
 459         }
 460
 461         _ => (/* pass */)
 462     }
 463 }
 464
 465 /// Helper for discovering nodes to check for stability
 466 pub fn check_expr(tcx: &ty::ctxt, e: &hir::Expr,
 467                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 468     let span;
 469     let id = match e.node {
 470         hir::ExprMethodCall(i, _, _) => {
 471             span = i.span;
 472             let method_call = ty::MethodCall::expr(e.id);
 473             tcx.tables.borrow().method_map[&method_call].def_id
 474         }
 475         hir::ExprField(ref base_e, ref field) => {
 476             span = field.span;
 477             match tcx.expr_ty_adjusted(base_e).sty {
 478                 ty::TyStruct(def, _) => def.struct_variant().field_named(field.node).did,
 479                 _ => tcx.sess.span_bug(e.span,
 480                                        "stability::check_expr: named field access on non-struct")
 481             }
 482         }
 483         hir::ExprTupField(ref base_e, ref field) => {
 484             span = field.span;
 485             match tcx.expr_ty_adjusted(base_e).sty {
 486                 ty::TyStruct(def, _) => def.struct_variant().fields[field.node].did,
 487                 ty::TyTuple(..) => return,
 488                 _ => tcx.sess.span_bug(e.span,
 489                                        "stability::check_expr: unnamed field access on \
 490                                         something other than a tuple or struct")
 491             }
 492         }
 493         hir::ExprStruct(_, ref expr_fields, _) => {
 494             let type_ = tcx.expr_ty(e);
 495             match type_.sty {
 496                 ty::TyStruct(def, _) => {
 497                     // check the stability of each field that appears
 498                     // in the construction expression.
 499                     for field in expr_fields {
 500                         let did = def.struct_variant()
 501                             .field_named(field.name.node)
 502                             .did;
 503                         maybe_do_stability_check(tcx, did, field.span, cb);
 504                     }
 505
 506                     // we're done.
 507                     return
 508                 }
 509                 // we don't look at stability attributes on
 510                 // struct-like enums (yet...), but it's definitely not
 511                 // a bug to have construct one.
 512                 ty::TyEnum(..) => return,
 513                 _ => {
 514                     tcx.sess.span_bug(e.span,
 515                                       &format!("stability::check_expr: struct construction \
 516                                                 of non-struct, type {:?}",
 517                                                type_));
 518                 }
 519             }
 520         }
 521         _ => return
 522     };
 523
 524     maybe_do_stability_check(tcx, id, span, cb);
 525 }
 526
 527 pub fn check_path(tcx: &ty::ctxt, path: &hir::Path, id: ast::NodeId,
 528                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 529     match tcx.def_map.borrow().get(&id).map(|d| d.full_def()) {
 530         Some(def::DefPrimTy(..)) => {}
 531         Some(def::DefSelfTy(..)) => {}
 532         Some(def) => {
 533             maybe_do_stability_check(tcx, def.def_id(), path.span, cb);
 534         }
 535         None => {}
 536     }
 537 }
 538
 539 pub fn check_path_list_item(tcx: &ty::ctxt, item: &hir::PathListItem,
 540                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 541     match tcx.def_map.borrow().get(&item.node.id()).map(|d| d.full_def()) {
 542         Some(def::DefPrimTy(..)) => {}
 543         Some(def) => {
 544             maybe_do_stability_check(tcx, def.def_id(), item.span, cb);
 545         }
 546         None => {}
 547     }
 548 }
 549
 550 pub fn check_pat(tcx: &ty::ctxt, pat: &hir::Pat,
 551                  cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 552     debug!("check_pat(pat = {:?})", pat);
 553     if is_internal(tcx, pat.span) { return; }
 554
 555     let v = match tcx.pat_ty_opt(pat) {
 556         Some(&ty::TyS { sty: ty::TyStruct(def, _), .. }) => def.struct_variant(),
 557         Some(_) | None => return,
 558     };
 559     match pat.node {
 560         // Foo(a, b, c)
 561         // A Variant(..) pattern `hir::PatEnum(_, None)` doesn't have to be recursed into.
 562         hir::PatEnum(_, Some(ref pat_fields)) => {
 563             for (field, struct_field) in pat_fields.iter().zip(&v.fields) {
 564                 maybe_do_stability_check(tcx, struct_field.did, field.span, cb)
 565             }
 566         }
 567         // Foo { a, b, c }
 568         hir::PatStruct(_, ref pat_fields, _) => {
 569             for field in pat_fields {
 570                 let did = v.field_named(field.node.name).did;
 571                 maybe_do_stability_check(tcx, did, field.span, cb);
 572             }
 573         }
 574         // everything else is fine.
 575         _ => {}
 576     }
 577 }
 578
 579 fn maybe_do_stability_check(tcx: &ty::ctxt, id: DefId, span: Span,
 580                             cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 581     if !is_staged_api(tcx, id) {
 582         debug!("maybe_do_stability_check: \
 583                 skipping id={:?} since it is not staged_api", id);
 584         return;
 585     }
 586     if is_internal(tcx, span) {
 587         debug!("maybe_do_stability_check: \
 588                 skipping span={:?} since it is internal", span);
 589         return;
 590     }
 591     let ref stability = lookup(tcx, id);
 592     debug!("maybe_do_stability_check: \
 593             inspecting id={:?} span={:?} of stability={:?}", id, span, stability);
 594     cb(id, span, stability);
 595 }
 596
 597 fn is_internal(tcx: &ty::ctxt, span: Span) -> bool {
 598     tcx.sess.codemap().span_allows_unstable(span)
 599 }
 600
 601 fn is_staged_api(tcx: &ty::ctxt, id: DefId) -> bool {
 602     match tcx.trait_item_of_item(id) {
 603         Some(ty::MethodTraitItemId(trait_method_id))
 604             if trait_method_id != id => {
 605                 is_staged_api(tcx, trait_method_id)
 606             }
 607         _ => {
 608             *tcx.stability.borrow_mut().staged_api.entry(id.krate).or_insert_with(
 609                 || csearch::is_staged_api(&tcx.sess.cstore, id.krate))
 610         }
 611     }
 612 }
 613
 614 /// Lookup the stability for a node, loading external crate
 615 /// metadata as necessary.
 616 pub fn lookup<'tcx>(tcx: &ty::ctxt<'tcx>, id: DefId) -> Option<&'tcx Stability> {
 617     if let Some(st) = tcx.stability.borrow().map.get(&id) {
 618         return *st;
 619     }
 620
 621     let st = lookup_uncached(tcx, id);
 622     tcx.stability.borrow_mut().map.insert(id, st);
 623     st
 624 }
 625
 626 fn lookup_uncached<'tcx>(tcx: &ty::ctxt<'tcx>, id: DefId) -> Option<&'tcx Stability> {
 627     debug!("lookup(id={:?})", id);
 628
 629     // is this definition the implementation of a trait method?
 630     match tcx.trait_item_of_item(id) {
 631         Some(ty::MethodTraitItemId(trait_method_id)) if trait_method_id != id => {
 632             debug!("lookup: trait_method_id={:?}", trait_method_id);
 633             return lookup(tcx, trait_method_id)
 634         }
 635         _ => {}
 636     }
 637
 638     let item_stab = if id.is_local() {
 639         None // The stability cache is filled partially lazily
 640     } else {
 641         csearch::get_stability(&tcx.sess.cstore, id).map(|st| tcx.intern_stability(st))
 642     };
 643
 644     item_stab.or_else(|| {
 645         if tcx.is_impl(id) {
 646             if let Some(trait_id) = tcx.trait_id_of_impl(id) {
 647                 // FIXME (#18969): for the time being, simply use the
 648                 // stability of the trait to determine the stability of any
 649                 // unmarked impls for it. See FIXME above for more details.
 650
 651                 debug!("lookup: trait_id={:?}", trait_id);
 652                 return lookup(tcx, trait_id);
 653             }
 654         }
 655         None
 656     })
 657 }
 658
 659 /// Given the list of enabled features that were not language features (i.e. that
 660 /// were expected to be library features), and the list of features used from
 661 /// libraries, identify activated features that don't exist and error about them.
 662 pub fn check_unused_or_stable_features(sess: &Session,
 663                                        lib_features_used: &FnvHashMap<InternedString,
 664                                                                       StabilityLevel>) {
 665     let ref declared_lib_features = sess.features.borrow().declared_lib_features;
 666     let mut remaining_lib_features: FnvHashMap<InternedString, Span>
 667         = declared_lib_features.clone().into_iter().collect();
 668
 669     let stable_msg = "this feature is stable. attribute no longer needed";
 670
 671     for &span in &sess.features.borrow().declared_stable_lang_features {
 672         sess.add_lint(lint::builtin::STABLE_FEATURES,
 673                       ast::CRATE_NODE_ID,
 674                       span,
 675                       stable_msg.to_string());
 676     }
 677
 678     for (used_lib_feature, level) in lib_features_used {
 679         match remaining_lib_features.remove(used_lib_feature) {
 680             Some(span) => {
 681                 if *level == Stable {
 682                     sess.add_lint(lint::builtin::STABLE_FEATURES,
 683                                   ast::CRATE_NODE_ID,
 684                                   span,
 685                                   stable_msg.to_string());
 686                 }
 687             }
 688             None => ( /* used but undeclared, handled during the previous ast visit */ )
 689         }
 690     }
 691
 692     for &span in remaining_lib_features.values() {
 693         sess.add_lint(lint::builtin::UNUSED_FEATURES,
 694                       ast::CRATE_NODE_ID,
 695                       span,
 696                       "unused or unknown feature".to_string());
 697     }
 698 }