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 session::Session;
  17 use lint;
  18 use middle::cstore::{CrateStore, LOCAL_CRATE};
  19 use middle::def;
  20 use middle::def_id::{CRATE_DEF_INDEX, DefId};
  21 use middle::ty;
  22 use middle::privacy::AccessLevels;
  23 use syntax::parse::token::InternedString;
  24 use syntax::codemap::{Span, DUMMY_SP};
  25 use syntax::ast;
  26 use syntax::ast::{NodeId, Attribute};
  27 use syntax::feature_gate::{GateIssue, emit_feature_err};
  28 use syntax::attr::{self, Stability, AttrMetaMethods};
  29 use util::nodemap::{DefIdMap, FnvHashSet, FnvHashMap};
  30
  31 use rustc_front::hir;
  32 use rustc_front::hir::{Block, Crate, Item, Generics, StructField, Variant};
  33 use rustc_front::intravisit::{self, Visitor};
  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 /// A stability index, giving the stability level for items and methods.
  61 pub struct Index<'tcx> {
  62     /// This is mostly a cache, except the stabilities of local items
  63     /// are filled by the annotator.
  64     map: DefIdMap<Option<&'tcx Stability>>,
  65
  66     /// Maps for each crate whether it is part of the staged API.
  67     staged_api: FnvHashMap<ast::CrateNum, bool>
  68 }
  69
  70 // A private tree-walker for producing an Index.
  71 struct Annotator<'a, 'tcx: 'a> {
  72     tcx: &'a ty::ctxt<'tcx>,
  73     index: &'a mut Index<'tcx>,
  74     parent: Option<&'tcx Stability>,
  75     access_levels: &'a AccessLevels,
  76     in_trait_impl: bool,
  77     in_enum: bool,
  78 }
  79
  80 impl<'a, 'tcx: 'a> Annotator<'a, 'tcx> {
  81     // Determine the stability for a node based on its attributes and inherited
  82     // stability. The stability is recorded in the index and used as the parent.
  83     fn annotate<F>(&mut self, id: NodeId, attrs: &Vec<Attribute>,
  84                    item_sp: Span, kind: AnnotationKind, visit_children: F)
  85         where F: FnOnce(&mut Annotator)
  86     {
  87         if self.index.staged_api[&LOCAL_CRATE] && self.tcx.sess.features.borrow().staged_api {
  88             debug!("annotate(id = {:?}, attrs = {:?})", id, attrs);
  89             if let Some(mut stab) = attr::find_stability(self.tcx.sess.diagnostic(),
  90                                                          attrs, item_sp) {
  91                 // Error if prohibited, or can't inherit anything from a container
  92                 if kind == AnnotationKind::Prohibited ||
  93                    (kind == AnnotationKind::Container &&
  94                     stab.level.is_stable() &&
  95                     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 == AnnotationKind::Required &&
 145                                    self.access_levels.is_reachable(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 == "rustc_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     /// Because stability levels are scoped lexically, we want to walk
 177     /// nested items in the context of the outer item, so enable
 178     /// deep-walking.
 179     fn visit_nested_item(&mut self, item: hir::ItemId) {
 180         self.visit_item(self.tcx.map.expect_item(item.id))
 181     }
 182
 183     fn visit_item(&mut self, i: &Item) {
 184         let orig_in_trait_impl = self.in_trait_impl;
 185         let orig_in_enum = self.in_enum;
 186         let mut kind = AnnotationKind::Required;
 187         match i.node {
 188             // Inherent impls and foreign modules serve only as containers for other items,
 189             // they don't have their own stability. They still can be annotated as unstable
 190             // and propagate this unstability to children, but this annotation is completely
 191             // optional. They inherit stability from their parents when unannotated.
 192             hir::ItemImpl(_, _, _, None, _, _) | hir::ItemForeignMod(..) => {
 193                 self.in_trait_impl = false;
 194                 kind = AnnotationKind::Container;
 195             }
 196             hir::ItemImpl(_, _, _, Some(_), _, _) => {
 197                 self.in_trait_impl = true;
 198             }
 199             hir::ItemStruct(ref sd, _) => {
 200                 self.in_enum = false;
 201                 if !sd.is_struct() {
 202                     self.annotate(sd.id(), &i.attrs, i.span, AnnotationKind::Required, |_| {})
 203                 }
 204             }
 205             hir::ItemEnum(..) => {
 206                 self.in_enum = true;
 207             }
 208             _ => {}
 209         }
 210
 211         self.annotate(i.id, &i.attrs, i.span, kind, |v| {
 212             intravisit::walk_item(v, i)
 213         });
 214         self.in_trait_impl = orig_in_trait_impl;
 215         self.in_enum = orig_in_enum;
 216     }
 217
 218     fn visit_trait_item(&mut self, ti: &hir::TraitItem) {
 219         self.annotate(ti.id, &ti.attrs, ti.span, AnnotationKind::Required, |v| {
 220             intravisit::walk_trait_item(v, ti);
 221         });
 222     }
 223
 224     fn visit_impl_item(&mut self, ii: &hir::ImplItem) {
 225         let kind = if self.in_trait_impl {
 226             AnnotationKind::Prohibited
 227         } else {
 228             AnnotationKind::Required
 229         };
 230         self.annotate(ii.id, &ii.attrs, ii.span, kind, |v| {
 231             intravisit::walk_impl_item(v, ii);
 232         });
 233     }
 234
 235     fn visit_variant(&mut self, var: &Variant, g: &'v Generics, item_id: NodeId) {
 236         self.annotate(var.node.data.id(), &var.node.attrs, var.span, AnnotationKind::Required, |v| {
 237             intravisit::walk_variant(v, var, g, item_id);
 238         })
 239     }
 240
 241     fn visit_struct_field(&mut self, s: &StructField) {
 242         // FIXME: This is temporary, can't use attributes with tuple variant fields until snapshot
 243         let kind = if self.in_enum && s.node.kind.is_unnamed() {
 244             AnnotationKind::Prohibited
 245         } else {
 246             AnnotationKind::Required
 247         };
 248         self.annotate(s.node.id, &s.node.attrs, s.span, kind, |v| {
 249             intravisit::walk_struct_field(v, s);
 250         });
 251     }
 252
 253     fn visit_foreign_item(&mut self, i: &hir::ForeignItem) {
 254         self.annotate(i.id, &i.attrs, i.span, AnnotationKind::Required, |v| {
 255             intravisit::walk_foreign_item(v, i);
 256         });
 257     }
 258
 259     fn visit_macro_def(&mut self, md: &'v hir::MacroDef) {
 260         if md.imported_from.is_none() {
 261             self.annotate(md.id, &md.attrs, md.span, AnnotationKind::Required, |_| {});
 262         }
 263     }
 264 }
 265
 266 impl<'tcx> Index<'tcx> {
 267     /// Construct the stability index for a crate being compiled.
 268     pub fn build(&mut self, tcx: &ty::ctxt<'tcx>, krate: &Crate, access_levels: &AccessLevels) {
 269         let mut annotator = Annotator {
 270             tcx: tcx,
 271             index: self,
 272             parent: None,
 273             access_levels: access_levels,
 274             in_trait_impl: false,
 275             in_enum: false,
 276         };
 277         annotator.annotate(ast::CRATE_NODE_ID, &krate.attrs, krate.span, AnnotationKind::Required,
 278                            |v| intravisit::walk_crate(v, krate));
 279     }
 280
 281     pub fn new(krate: &Crate) -> Index<'tcx> {
 282         let mut is_staged_api = false;
 283         for attr in &krate.attrs {
 284             if attr.name() == "stable" || attr.name() == "unstable" {
 285                 is_staged_api = true;
 286                 break
 287             }
 288         }
 289
 290         let mut staged_api = FnvHashMap();
 291         staged_api.insert(LOCAL_CRATE, is_staged_api);
 292         Index {
 293             staged_api: staged_api,
 294             map: DefIdMap(),
 295         }
 296     }
 297 }
 298
 299 /// Cross-references the feature names of unstable APIs with enabled
 300 /// features and possibly prints errors. Returns a list of all
 301 /// features used.
 302 pub fn check_unstable_api_usage(tcx: &ty::ctxt)
 303                                 -> FnvHashMap<InternedString, StabilityLevel> {
 304     let ref active_lib_features = tcx.sess.features.borrow().declared_lib_features;
 305
 306     // Put the active features into a map for quick lookup
 307     let active_features = active_lib_features.iter().map(|&(ref s, _)| s.clone()).collect();
 308
 309     let mut checker = Checker {
 310         tcx: tcx,
 311         active_features: active_features,
 312         used_features: FnvHashMap(),
 313         in_skip_block: 0,
 314     };
 315     intravisit::walk_crate(&mut checker, tcx.map.krate());
 316
 317     let used_features = checker.used_features;
 318     return used_features;
 319 }
 320
 321 struct Checker<'a, 'tcx: 'a> {
 322     tcx: &'a ty::ctxt<'tcx>,
 323     active_features: FnvHashSet<InternedString>,
 324     used_features: FnvHashMap<InternedString, StabilityLevel>,
 325     // Within a block where feature gate checking can be skipped.
 326     in_skip_block: u32,
 327 }
 328
 329 impl<'a, 'tcx> Checker<'a, 'tcx> {
 330     fn check(&mut self, id: DefId, span: Span, stab: &Option<&Stability>) {
 331         // Only the cross-crate scenario matters when checking unstable APIs
 332         let cross_crate = !id.is_local();
 333         if !cross_crate {
 334             return
 335         }
 336
 337         // We don't need to check for stability - presumably compiler generated code.
 338         if self.in_skip_block > 0 {
 339             return;
 340         }
 341
 342         match *stab {
 343             Some(&Stability { level: attr::Unstable {ref reason, issue}, ref feature, .. }) => {
 344                 self.used_features.insert(feature.clone(), Unstable);
 345
 346                 if !self.active_features.contains(feature) {
 347                     let msg = match *reason {
 348                         Some(ref r) => format!("use of unstable library feature '{}': {}",
 349                                                &feature, &r),
 350                         None => format!("use of unstable library feature '{}'", &feature)
 351                     };
 352                     emit_feature_err(&self.tcx.sess.parse_sess.span_diagnostic,
 353                                       &feature, span, GateIssue::Library(Some(issue)), &msg);
 354                 }
 355             }
 356             Some(&Stability { ref level, ref feature, .. }) => {
 357                 self.used_features.insert(feature.clone(), StabilityLevel::from_attr_level(level));
 358
 359                 // Stable APIs are always ok to call and deprecated APIs are
 360                 // handled by a lint.
 361             }
 362             None => {
 363                 // This is an 'unmarked' API, which should not exist
 364                 // in the standard library.
 365                 if self.tcx.sess.features.borrow().unmarked_api {
 366                     self.tcx.sess.span_warn(span, "use of unmarked library feature");
 367                     self.tcx.sess.span_note(span, "this is either a bug in the library you are \
 368                                                    using or a bug in the compiler - please \
 369                                                    report it in both places");
 370                 } else {
 371                     self.tcx.sess.span_err(span, "use of unmarked library feature");
 372                     self.tcx.sess.span_note(span, "this is either a bug in the library you are \
 373                                                    using or a bug in the compiler - please \
 374                                                    report it in both places");
 375                     self.tcx.sess.span_note(span, "use #![feature(unmarked_api)] in the \
 376                                                    crate attributes to override this");
 377                 }
 378             }
 379         }
 380     }
 381 }
 382
 383 impl<'a, 'v, 'tcx> Visitor<'v> for Checker<'a, 'tcx> {
 384     /// Because stability levels are scoped lexically, we want to walk
 385     /// nested items in the context of the outer item, so enable
 386     /// deep-walking.
 387     fn visit_nested_item(&mut self, item: hir::ItemId) {
 388         self.visit_item(self.tcx.map.expect_item(item.id))
 389     }
 390
 391     fn visit_item(&mut self, item: &hir::Item) {
 392         // When compiling with --test we don't enforce stability on the
 393         // compiler-generated test module, demarcated with `DUMMY_SP` plus the
 394         // name `__test`
 395         if item.span == DUMMY_SP && item.name.as_str() == "__test" { return }
 396
 397         check_item(self.tcx, item, true,
 398                    &mut |id, sp, stab| self.check(id, sp, stab));
 399         intravisit::walk_item(self, item);
 400     }
 401
 402     fn visit_expr(&mut self, ex: &hir::Expr) {
 403         check_expr(self.tcx, ex,
 404                    &mut |id, sp, stab| self.check(id, sp, stab));
 405         intravisit::walk_expr(self, ex);
 406     }
 407
 408     fn visit_path(&mut self, path: &hir::Path, id: ast::NodeId) {
 409         check_path(self.tcx, path, id,
 410                    &mut |id, sp, stab| self.check(id, sp, stab));
 411         intravisit::walk_path(self, path)
 412     }
 413
 414     fn visit_path_list_item(&mut self, prefix: &hir::Path, item: &hir::PathListItem) {
 415         check_path_list_item(self.tcx, item,
 416                    &mut |id, sp, stab| self.check(id, sp, stab));
 417         intravisit::walk_path_list_item(self, prefix, item)
 418     }
 419
 420     fn visit_pat(&mut self, pat: &hir::Pat) {
 421         check_pat(self.tcx, pat,
 422                   &mut |id, sp, stab| self.check(id, sp, stab));
 423         intravisit::walk_pat(self, pat)
 424     }
 425
 426     fn visit_block(&mut self, b: &hir::Block) {
 427         let old_skip_count = self.in_skip_block;
 428         match b.rules {
 429             hir::BlockCheckMode::PushUnstableBlock => {
 430                 self.in_skip_block += 1;
 431             }
 432             hir::BlockCheckMode::PopUnstableBlock => {
 433                 self.in_skip_block = self.in_skip_block.checked_sub(1).unwrap();
 434             }
 435             _ => {}
 436         }
 437         intravisit::walk_block(self, b);
 438         self.in_skip_block = old_skip_count;
 439     }
 440 }
 441
 442 /// Helper for discovering nodes to check for stability
 443 pub fn check_item(tcx: &ty::ctxt, item: &hir::Item, warn_about_defns: bool,
 444                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 445     match item.node {
 446         hir::ItemExternCrate(_) => {
 447             // compiler-generated `extern crate` items have a dummy span.
 448             if item.span == DUMMY_SP { return }
 449
 450             let cnum = match tcx.sess.cstore.extern_mod_stmt_cnum(item.id) {
 451                 Some(cnum) => cnum,
 452                 None => return,
 453             };
 454             let id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
 455             maybe_do_stability_check(tcx, id, item.span, cb);
 456         }
 457
 458         // For implementations of traits, check the stability of each item
 459         // individually as it's possible to have a stable trait with unstable
 460         // items.
 461         hir::ItemImpl(_, _, _, Some(ref t), _, ref impl_items) => {
 462             let trait_did = tcx.def_map.borrow().get(&t.ref_id).unwrap().def_id();
 463             let trait_items = tcx.trait_items(trait_did);
 464
 465             for impl_item in impl_items {
 466                 let item = trait_items.iter().find(|item| {
 467                     item.name() == impl_item.name
 468                 }).unwrap();
 469                 if warn_about_defns {
 470                     maybe_do_stability_check(tcx, item.def_id(), impl_item.span, cb);
 471                 }
 472             }
 473         }
 474
 475         _ => (/* pass */)
 476     }
 477 }
 478
 479 /// Helper for discovering nodes to check for stability
 480 pub fn check_expr(tcx: &ty::ctxt, e: &hir::Expr,
 481                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 482     let span;
 483     let id = match e.node {
 484         hir::ExprMethodCall(i, _, _) => {
 485             span = i.span;
 486             let method_call = ty::MethodCall::expr(e.id);
 487             tcx.tables.borrow().method_map[&method_call].def_id
 488         }
 489         hir::ExprField(ref base_e, ref field) => {
 490             span = field.span;
 491             match tcx.expr_ty_adjusted(base_e).sty {
 492                 ty::TyStruct(def, _) => def.struct_variant().field_named(field.node).did,
 493                 _ => tcx.sess.span_bug(e.span,
 494                                        "stability::check_expr: named field access on non-struct")
 495             }
 496         }
 497         hir::ExprTupField(ref base_e, ref field) => {
 498             span = field.span;
 499             match tcx.expr_ty_adjusted(base_e).sty {
 500                 ty::TyStruct(def, _) => def.struct_variant().fields[field.node].did,
 501                 ty::TyTuple(..) => return,
 502                 _ => tcx.sess.span_bug(e.span,
 503                                        "stability::check_expr: unnamed field access on \
 504                                         something other than a tuple or struct")
 505             }
 506         }
 507         hir::ExprStruct(_, ref expr_fields, _) => {
 508             let type_ = tcx.expr_ty(e);
 509             match type_.sty {
 510                 ty::TyStruct(def, _) => {
 511                     // check the stability of each field that appears
 512                     // in the construction expression.
 513                     for field in expr_fields {
 514                         let did = def.struct_variant()
 515                             .field_named(field.name.node)
 516                             .did;
 517                         maybe_do_stability_check(tcx, did, field.span, cb);
 518                     }
 519
 520                     // we're done.
 521                     return
 522                 }
 523                 // we don't look at stability attributes on
 524                 // struct-like enums (yet...), but it's definitely not
 525                 // a bug to have construct one.
 526                 ty::TyEnum(..) => return,
 527                 _ => {
 528                     tcx.sess.span_bug(e.span,
 529                                       &format!("stability::check_expr: struct construction \
 530                                                 of non-struct, type {:?}",
 531                                                type_));
 532                 }
 533             }
 534         }
 535         _ => return
 536     };
 537
 538     maybe_do_stability_check(tcx, id, span, cb);
 539 }
 540
 541 pub fn check_path(tcx: &ty::ctxt, path: &hir::Path, id: ast::NodeId,
 542                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 543     match tcx.def_map.borrow().get(&id).map(|d| d.full_def()) {
 544         Some(def::DefPrimTy(..)) => {}
 545         Some(def::DefSelfTy(..)) => {}
 546         Some(def) => {
 547             maybe_do_stability_check(tcx, def.def_id(), path.span, cb);
 548         }
 549         None => {}
 550     }
 551 }
 552
 553 pub fn check_path_list_item(tcx: &ty::ctxt, item: &hir::PathListItem,
 554                   cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 555     match tcx.def_map.borrow().get(&item.node.id()).map(|d| d.full_def()) {
 556         Some(def::DefPrimTy(..)) => {}
 557         Some(def) => {
 558             maybe_do_stability_check(tcx, def.def_id(), item.span, cb);
 559         }
 560         None => {}
 561     }
 562 }
 563
 564 pub fn check_pat(tcx: &ty::ctxt, pat: &hir::Pat,
 565                  cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 566     debug!("check_pat(pat = {:?})", pat);
 567     if is_internal(tcx, pat.span) { return; }
 568
 569     let v = match tcx.pat_ty_opt(pat) {
 570         Some(&ty::TyS { sty: ty::TyStruct(def, _), .. }) => def.struct_variant(),
 571         Some(_) | None => return,
 572     };
 573     match pat.node {
 574         // Foo(a, b, c)
 575         // A Variant(..) pattern `hir::PatEnum(_, None)` doesn't have to be recursed into.
 576         hir::PatEnum(_, Some(ref pat_fields)) => {
 577             for (field, struct_field) in pat_fields.iter().zip(&v.fields) {
 578                 maybe_do_stability_check(tcx, struct_field.did, field.span, cb)
 579             }
 580         }
 581         // Foo { a, b, c }
 582         hir::PatStruct(_, ref pat_fields, _) => {
 583             for field in pat_fields {
 584                 let did = v.field_named(field.node.name).did;
 585                 maybe_do_stability_check(tcx, did, field.span, cb);
 586             }
 587         }
 588         // everything else is fine.
 589         _ => {}
 590     }
 591 }
 592
 593 fn maybe_do_stability_check(tcx: &ty::ctxt, id: DefId, span: Span,
 594                             cb: &mut FnMut(DefId, Span, &Option<&Stability>)) {
 595     if !is_staged_api(tcx, id) {
 596         debug!("maybe_do_stability_check: \
 597                 skipping id={:?} since it is not staged_api", id);
 598         return;
 599     }
 600     if is_internal(tcx, span) {
 601         debug!("maybe_do_stability_check: \
 602                 skipping span={:?} since it is internal", span);
 603         return;
 604     }
 605     let ref stability = lookup(tcx, id);
 606     debug!("maybe_do_stability_check: \
 607             inspecting id={:?} span={:?} of stability={:?}", id, span, stability);
 608     cb(id, span, stability);
 609 }
 610
 611 fn is_internal(tcx: &ty::ctxt, span: Span) -> bool {
 612     tcx.sess.codemap().span_allows_unstable(span)
 613 }
 614
 615 fn is_staged_api(tcx: &ty::ctxt, id: DefId) -> bool {
 616     match tcx.trait_item_of_item(id) {
 617         Some(ty::MethodTraitItemId(trait_method_id))
 618             if trait_method_id != id => {
 619                 is_staged_api(tcx, trait_method_id)
 620             }
 621         _ => {
 622             *tcx.stability.borrow_mut().staged_api.entry(id.krate).or_insert_with(
 623                 || tcx.sess.cstore.is_staged_api(id.krate))
 624         }
 625     }
 626 }
 627
 628 /// Lookup the stability for a node, loading external crate
 629 /// metadata as necessary.
 630 pub fn lookup<'tcx>(tcx: &ty::ctxt<'tcx>, id: DefId) -> Option<&'tcx Stability> {
 631     if let Some(st) = tcx.stability.borrow().map.get(&id) {
 632         return *st;
 633     }
 634
 635     let st = lookup_uncached(tcx, id);
 636     tcx.stability.borrow_mut().map.insert(id, st);
 637     st
 638 }
 639
 640 fn lookup_uncached<'tcx>(tcx: &ty::ctxt<'tcx>, id: DefId) -> Option<&'tcx Stability> {
 641     debug!("lookup(id={:?})", id);
 642
 643     // is this definition the implementation of a trait method?
 644     match tcx.trait_item_of_item(id) {
 645         Some(ty::MethodTraitItemId(trait_method_id)) if trait_method_id != id => {
 646             debug!("lookup: trait_method_id={:?}", trait_method_id);
 647             return lookup(tcx, trait_method_id)
 648         }
 649         _ => {}
 650     }
 651
 652     let item_stab = if id.is_local() {
 653         None // The stability cache is filled partially lazily
 654     } else {
 655         tcx.sess.cstore.stability(id).map(|st| tcx.intern_stability(st))
 656     };
 657
 658     item_stab.or_else(|| {
 659         if tcx.is_impl(id) {
 660             if let Some(trait_id) = tcx.trait_id_of_impl(id) {
 661                 // FIXME (#18969): for the time being, simply use the
 662                 // stability of the trait to determine the stability of any
 663                 // unmarked impls for it. See FIXME above for more details.
 664
 665                 debug!("lookup: trait_id={:?}", trait_id);
 666                 return lookup(tcx, trait_id);
 667             }
 668         }
 669         None
 670     })
 671 }
 672
 673 /// Given the list of enabled features that were not language features (i.e. that
 674 /// were expected to be library features), and the list of features used from
 675 /// libraries, identify activated features that don't exist and error about them.
 676 pub fn check_unused_or_stable_features(sess: &Session,
 677                                        lib_features_used: &FnvHashMap<InternedString,
 678                                                                       StabilityLevel>) {
 679     let ref declared_lib_features = sess.features.borrow().declared_lib_features;
 680     let mut remaining_lib_features: FnvHashMap<InternedString, Span>
 681         = declared_lib_features.clone().into_iter().collect();
 682
 683     let stable_msg = "this feature is stable. attribute no longer needed";
 684
 685     for &span in &sess.features.borrow().declared_stable_lang_features {
 686         sess.add_lint(lint::builtin::STABLE_FEATURES,
 687                       ast::CRATE_NODE_ID,
 688                       span,
 689                       stable_msg.to_string());
 690     }
 691
 692     for (used_lib_feature, level) in lib_features_used {
 693         match remaining_lib_features.remove(used_lib_feature) {
 694             Some(span) => {
 695                 if *level == Stable {
 696                     sess.add_lint(lint::builtin::STABLE_FEATURES,
 697                                   ast::CRATE_NODE_ID,
 698                                   span,
 699                                   stable_msg.to_string());
 700                 }
 701             }
 702             None => ( /* used but undeclared, handled during the previous ast visit */ )
 703         }
 704     }
 705
 706     for &span in remaining_lib_features.values() {
 707         sess.add_lint(lint::builtin::UNUSED_FEATURES,
 708                       ast::CRATE_NODE_ID,
 709                       span,
 710                       "unused or unknown feature".to_string());
 711     }
 712 }