src/librustc/middle/dead.rs

   1 // Copyright 2013 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 // This implements the dead-code warning pass. It follows middle::reachable
  12 // closely. The idea is that all reachable symbols are live, codes called
  13 // from live codes are live, and everything else is dead.
  14
  15 use hir::map as hir_map;
  16 use hir::{self, Item_, PatKind};
  17 use hir::intravisit::{self, Visitor, NestedVisitorMap};
  18 use hir::itemlikevisit::ItemLikeVisitor;
  19
  20 use hir::def::Def;
  21 use hir::def_id::{DefId, LOCAL_CRATE};
  22 use lint;
  23 use middle::privacy;
  24 use ty::{self, TyCtxt};
  25 use util::nodemap::FxHashSet;
  26
  27 use syntax::{ast, codemap};
  28 use syntax::attr;
  29 use syntax_pos;
  30
  31 // Any local node that may call something in its body block should be
  32 // explored. For example, if it's a live NodeItem that is a
  33 // function, then we should explore its block to check for codes that
  34 // may need to be marked as live.
  35 fn should_explore<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  36                             node_id: ast::NodeId) -> bool {
  37     match tcx.hir.find(node_id) {
  38         Some(hir_map::NodeItem(..)) |
  39         Some(hir_map::NodeImplItem(..)) |
  40         Some(hir_map::NodeForeignItem(..)) |
  41         Some(hir_map::NodeTraitItem(..)) =>
  42             true,
  43         _ =>
  44             false
  45     }
  46 }
  47
  48 struct MarkSymbolVisitor<'a, 'tcx: 'a> {
  49     worklist: Vec<ast::NodeId>,
  50     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  51     tables: &'a ty::TypeckTables<'tcx>,
  52     live_symbols: Box<FxHashSet<ast::NodeId>>,
  53     struct_has_extern_repr: bool,
  54     in_pat: bool,
  55     inherited_pub_visibility: bool,
  56     ignore_variant_stack: Vec<DefId>,
  57 }
  58
  59 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
  60     fn check_def_id(&mut self, def_id: DefId) {
  61         if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
  62             if should_explore(self.tcx, node_id) {
  63                 self.worklist.push(node_id);
  64             }
  65             self.live_symbols.insert(node_id);
  66         }
  67     }
  68
  69     fn insert_def_id(&mut self, def_id: DefId) {
  70         if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
  71             debug_assert!(!should_explore(self.tcx, node_id));
  72             self.live_symbols.insert(node_id);
  73         }
  74     }
  75
  76     fn handle_definition(&mut self, def: Def) {
  77         match def {
  78             Def::Const(_) | Def::AssociatedConst(..) | Def::TyAlias(_) => {
  79                 self.check_def_id(def.def_id());
  80             }
  81             _ if self.in_pat => (),
  82             Def::PrimTy(..) | Def::SelfTy(..) |
  83             Def::Local(..) | Def::Upvar(..) => {}
  84             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
  85                 if let Some(enum_id) = self.tcx.parent_def_id(variant_id) {
  86                     self.check_def_id(enum_id);
  87                 }
  88                 if !self.ignore_variant_stack.contains(&variant_id) {
  89                     self.check_def_id(variant_id);
  90                 }
  91             }
  92             _ => {
  93                 self.check_def_id(def.def_id());
  94             }
  95         }
  96     }
  97
  98     fn lookup_and_handle_method(&mut self, id: hir::HirId) {
  99         self.check_def_id(self.tables.type_dependent_defs()[id].def_id());
 100     }
 101
 102     fn handle_field_access(&mut self, lhs: &hir::Expr, name: ast::Name) {
 103         match self.tables.expr_ty_adjusted(lhs).sty {
 104             ty::TyAdt(def, _) => {
 105                 self.insert_def_id(def.struct_variant().field_named(name).did);
 106             }
 107             _ => span_bug!(lhs.span, "named field access on non-ADT"),
 108         }
 109     }
 110
 111     fn handle_tup_field_access(&mut self, lhs: &hir::Expr, idx: usize) {
 112         match self.tables.expr_ty_adjusted(lhs).sty {
 113             ty::TyAdt(def, _) => {
 114                 self.insert_def_id(def.struct_variant().fields[idx].did);
 115             }
 116             ty::TyTuple(..) => {}
 117             _ => span_bug!(lhs.span, "numeric field access on non-ADT"),
 118         }
 119     }
 120
 121     fn handle_field_pattern_match(&mut self, lhs: &hir::Pat, def: Def,
 122                                   pats: &[codemap::Spanned<hir::FieldPat>]) {
 123         let variant = match self.tables.node_id_to_type(lhs.hir_id).sty {
 124             ty::TyAdt(adt, _) => adt.variant_of_def(def),
 125             _ => span_bug!(lhs.span, "non-ADT in struct pattern")
 126         };
 127         for pat in pats {
 128             if let PatKind::Wild = pat.node.pat.node {
 129                 continue;
 130             }
 131             self.insert_def_id(variant.field_named(pat.node.name).did);
 132         }
 133     }
 134
 135     fn mark_live_symbols(&mut self) {
 136         let mut scanned = FxHashSet();
 137         while !self.worklist.is_empty() {
 138             let id = self.worklist.pop().unwrap();
 139             if scanned.contains(&id) {
 140                 continue
 141             }
 142             scanned.insert(id);
 143
 144             if let Some(ref node) = self.tcx.hir.find(id) {
 145                 self.live_symbols.insert(id);
 146                 self.visit_node(node);
 147             }
 148         }
 149     }
 150
 151     fn visit_node(&mut self, node: &hir_map::Node<'tcx>) {
 152         let had_extern_repr = self.struct_has_extern_repr;
 153         self.struct_has_extern_repr = false;
 154         let had_inherited_pub_visibility = self.inherited_pub_visibility;
 155         self.inherited_pub_visibility = false;
 156         match *node {
 157             hir_map::NodeItem(item) => {
 158                 match item.node {
 159                     hir::ItemStruct(..) | hir::ItemUnion(..) => {
 160                         let def_id = self.tcx.hir.local_def_id(item.id);
 161                         let def = self.tcx.adt_def(def_id);
 162                         self.struct_has_extern_repr = def.repr.c();
 163
 164                         intravisit::walk_item(self, &item);
 165                     }
 166                     hir::ItemEnum(..) => {
 167                         self.inherited_pub_visibility = item.vis == hir::Public;
 168                         intravisit::walk_item(self, &item);
 169                     }
 170                     hir::ItemFn(..)
 171                     | hir::ItemTy(..)
 172                     | hir::ItemStatic(..)
 173                     | hir::ItemConst(..) => {
 174                         intravisit::walk_item(self, &item);
 175                     }
 176                     _ => ()
 177                 }
 178             }
 179             hir_map::NodeTraitItem(trait_item) => {
 180                 intravisit::walk_trait_item(self, trait_item);
 181             }
 182             hir_map::NodeImplItem(impl_item) => {
 183                 intravisit::walk_impl_item(self, impl_item);
 184             }
 185             hir_map::NodeForeignItem(foreign_item) => {
 186                 intravisit::walk_foreign_item(self, &foreign_item);
 187             }
 188             _ => ()
 189         }
 190         self.struct_has_extern_repr = had_extern_repr;
 191         self.inherited_pub_visibility = had_inherited_pub_visibility;
 192     }
 193
 194     fn mark_as_used_if_union(&mut self, did: DefId, fields: &hir::HirVec<hir::Field>) {
 195         if let Some(node_id) = self.tcx.hir.as_local_node_id(did) {
 196             if let Some(hir_map::NodeItem(item)) = self.tcx.hir.find(node_id) {
 197                 if let Item_::ItemUnion(ref variant, _) = item.node {
 198                     if variant.fields().len() > 1 {
 199                         for field in variant.fields() {
 200                             if fields.iter().find(|x| x.name.node == field.name).is_some() {
 201                                 self.live_symbols.insert(field.id);
 202                             }
 203                         }
 204                     }
 205                 }
 206             }
 207         }
 208     }
 209 }
 210
 211 impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
 212     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 213         NestedVisitorMap::None
 214     }
 215
 216     fn visit_nested_body(&mut self, body: hir::BodyId) {
 217         let old_tables = self.tables;
 218         self.tables = self.tcx.body_tables(body);
 219         let body = self.tcx.hir.body(body);
 220         self.visit_body(body);
 221         self.tables = old_tables;
 222     }
 223
 224     fn visit_variant_data(&mut self, def: &'tcx hir::VariantData, _: ast::Name,
 225                         _: &hir::Generics, _: ast::NodeId, _: syntax_pos::Span) {
 226         let has_extern_repr = self.struct_has_extern_repr;
 227         let inherited_pub_visibility = self.inherited_pub_visibility;
 228         let live_fields = def.fields().iter().filter(|f| {
 229             has_extern_repr || inherited_pub_visibility || f.vis == hir::Public
 230         });
 231         self.live_symbols.extend(live_fields.map(|f| f.id));
 232
 233         intravisit::walk_struct_def(self, def);
 234     }
 235
 236     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 237         match expr.node {
 238             hir::ExprPath(ref qpath @ hir::QPath::TypeRelative(..)) => {
 239                 let def = self.tables.qpath_def(qpath, expr.hir_id);
 240                 self.handle_definition(def);
 241             }
 242             hir::ExprMethodCall(..) => {
 243                 self.lookup_and_handle_method(expr.hir_id);
 244             }
 245             hir::ExprField(ref lhs, ref name) => {
 246                 self.handle_field_access(&lhs, name.node);
 247             }
 248             hir::ExprTupField(ref lhs, idx) => {
 249                 self.handle_tup_field_access(&lhs, idx.node);
 250             }
 251             hir::ExprStruct(_, ref fields, _) => {
 252                 if let ty::TypeVariants::TyAdt(ref def, _) = self.tables.expr_ty(expr).sty {
 253                     if def.is_union() {
 254                         self.mark_as_used_if_union(def.did, fields);
 255                     }
 256                 }
 257             }
 258             _ => ()
 259         }
 260
 261         intravisit::walk_expr(self, expr);
 262     }
 263
 264     fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
 265         if arm.pats.len() == 1 {
 266             let variants = arm.pats[0].necessary_variants();
 267
 268             // Inside the body, ignore constructions of variants
 269             // necessary for the pattern to match. Those construction sites
 270             // can't be reached unless the variant is constructed elsewhere.
 271             let len = self.ignore_variant_stack.len();
 272             self.ignore_variant_stack.extend_from_slice(&variants);
 273             intravisit::walk_arm(self, arm);
 274             self.ignore_variant_stack.truncate(len);
 275         } else {
 276             intravisit::walk_arm(self, arm);
 277         }
 278     }
 279
 280     fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
 281         match pat.node {
 282             PatKind::Struct(hir::QPath::Resolved(_, ref path), ref fields, _) => {
 283                 self.handle_field_pattern_match(pat, path.def, fields);
 284             }
 285             PatKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
 286                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 287                 self.handle_definition(def);
 288             }
 289             _ => ()
 290         }
 291
 292         self.in_pat = true;
 293         intravisit::walk_pat(self, pat);
 294         self.in_pat = false;
 295     }
 296
 297     fn visit_path(&mut self, path: &'tcx hir::Path, _: ast::NodeId) {
 298         self.handle_definition(path.def);
 299         intravisit::walk_path(self, path);
 300     }
 301 }
 302
 303 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt,
 304                                     id: ast::NodeId,
 305                                     attrs: &[ast::Attribute]) -> bool {
 306     if attr::contains_name(attrs, "lang") {
 307         return true;
 308     }
 309
 310     // #[used] also keeps the item alive forcefully,
 311     // e.g. for placing it in a specific section.
 312     if attr::contains_name(attrs, "used") {
 313         return true;
 314     }
 315
 316     // Don't lint about global allocators
 317     if attr::contains_name(attrs, "global_allocator") {
 318         return true;
 319     }
 320
 321     tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
 322 }
 323
 324 // This visitor seeds items that
 325 //   1) We want to explicitly consider as live:
 326 //     * Item annotated with #[allow(dead_code)]
 327 //         - This is done so that if we want to suppress warnings for a
 328 //           group of dead functions, we only have to annotate the "root".
 329 //           For example, if both `f` and `g` are dead and `f` calls `g`,
 330 //           then annotating `f` with `#[allow(dead_code)]` will suppress
 331 //           warning for both `f` and `g`.
 332 //     * Item annotated with #[lang=".."]
 333 //         - This is because lang items are always callable from elsewhere.
 334 //   or
 335 //   2) We are not sure to be live or not
 336 //     * Implementation of a trait method
 337 struct LifeSeeder<'k, 'tcx: 'k> {
 338     worklist: Vec<ast::NodeId>,
 339     krate: &'k hir::Crate,
 340     tcx: TyCtxt<'k, 'tcx, 'tcx>,
 341 }
 342
 343 impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
 344     fn visit_item(&mut self, item: &hir::Item) {
 345         let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx,
 346                                                                item.id,
 347                                                                &item.attrs);
 348         if allow_dead_code {
 349             self.worklist.push(item.id);
 350         }
 351         match item.node {
 352             hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
 353                 self.worklist.extend(enum_def.variants.iter()
 354                                                       .map(|variant| variant.node.data.id()));
 355             }
 356             hir::ItemTrait(.., ref trait_item_refs) => {
 357                 for trait_item_ref in trait_item_refs {
 358                     let trait_item = self.krate.trait_item(trait_item_ref.id);
 359                     match trait_item.node {
 360                         hir::TraitItemKind::Const(_, Some(_)) |
 361                         hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
 362                             if has_allow_dead_code_or_lang_attr(self.tcx,
 363                                                                 trait_item.id,
 364                                                                 &trait_item.attrs) {
 365                                 self.worklist.push(trait_item.id);
 366                             }
 367                         }
 368                         _ => {}
 369                     }
 370                 }
 371             }
 372             hir::ItemImpl(.., ref opt_trait, _, ref impl_item_refs) => {
 373                 for impl_item_ref in impl_item_refs {
 374                     let impl_item = self.krate.impl_item(impl_item_ref.id);
 375                     if opt_trait.is_some() ||
 376                             has_allow_dead_code_or_lang_attr(self.tcx,
 377                                                              impl_item.id,
 378                                                              &impl_item.attrs) {
 379                         self.worklist.push(impl_item_ref.id.node_id);
 380                     }
 381                 }
 382             }
 383             _ => ()
 384         }
 385     }
 386
 387     fn visit_trait_item(&mut self, _item: &hir::TraitItem) {
 388         // ignore: we are handling this in `visit_item` above
 389     }
 390
 391     fn visit_impl_item(&mut self, _item: &hir::ImplItem) {
 392         // ignore: we are handling this in `visit_item` above
 393     }
 394 }
 395
 396 fn create_and_seed_worklist<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 397                                       access_levels: &privacy::AccessLevels,
 398                                       krate: &hir::Crate)
 399                                       -> Vec<ast::NodeId> {
 400     let mut worklist = Vec::new();
 401     for (id, _) in &access_levels.map {
 402         worklist.push(*id);
 403     }
 404
 405     // Seed entry point
 406     if let Some((id, _)) = *tcx.sess.entry_fn.borrow() {
 407         worklist.push(id);
 408     }
 409
 410     // Seed implemented trait items
 411     let mut life_seeder = LifeSeeder {
 412         worklist,
 413         krate,
 414         tcx,
 415     };
 416     krate.visit_all_item_likes(&mut life_seeder);
 417
 418     return life_seeder.worklist;
 419 }
 420
 421 fn find_live<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 422                        access_levels: &privacy::AccessLevels,
 423                        krate: &hir::Crate)
 424                        -> Box<FxHashSet<ast::NodeId>> {
 425     let worklist = create_and_seed_worklist(tcx, access_levels, krate);
 426     let mut symbol_visitor = MarkSymbolVisitor {
 427         worklist,
 428         tcx,
 429         tables: &ty::TypeckTables::empty(None),
 430         live_symbols: box FxHashSet(),
 431         struct_has_extern_repr: false,
 432         in_pat: false,
 433         inherited_pub_visibility: false,
 434         ignore_variant_stack: vec![],
 435     };
 436     symbol_visitor.mark_live_symbols();
 437     symbol_visitor.live_symbols
 438 }
 439
 440 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
 441     match item.node {
 442         hir::ItemStruct(ref struct_def, _) if !struct_def.is_struct() => {
 443             Some(struct_def.id())
 444         }
 445         _ => None
 446     }
 447 }
 448
 449 struct DeadVisitor<'a, 'tcx: 'a> {
 450     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 451     live_symbols: Box<FxHashSet<ast::NodeId>>,
 452 }
 453
 454 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
 455     fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
 456         let should_warn = match item.node {
 457             hir::ItemStatic(..)
 458             | hir::ItemConst(..)
 459             | hir::ItemFn(..)
 460             | hir::ItemTy(..)
 461             | hir::ItemEnum(..)
 462             | hir::ItemStruct(..)
 463             | hir::ItemUnion(..) => true,
 464             _ => false
 465         };
 466         let ctor_id = get_struct_ctor_id(item);
 467         should_warn && !self.symbol_is_live(item.id, ctor_id)
 468     }
 469
 470     fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
 471         let field_type = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 472         let is_marker_field = match field_type.ty_to_def_id() {
 473             Some(def_id) => self.tcx.lang_items().items().iter().any(|item| *item == Some(def_id)),
 474             _ => false
 475         };
 476         !field.is_positional()
 477             && !self.symbol_is_live(field.id, None)
 478             && !is_marker_field
 479             && !has_allow_dead_code_or_lang_attr(self.tcx, field.id, &field.attrs)
 480     }
 481
 482     fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
 483         !self.symbol_is_live(variant.data.id(), None)
 484             && !has_allow_dead_code_or_lang_attr(self.tcx,
 485                                                  variant.data.id(),
 486                                                  &variant.attrs)
 487     }
 488
 489     fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem) -> bool {
 490         !self.symbol_is_live(fi.id, None)
 491             && !has_allow_dead_code_or_lang_attr(self.tcx, fi.id, &fi.attrs)
 492     }
 493
 494     // id := node id of an item's definition.
 495     // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
 496     //            `None` otherwise.
 497     // If the item is a struct_ctor, then either its `id` or
 498     // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
 499     // DefMap maps the ExprPath of a struct_ctor to the node referred by
 500     // `ctor_id`. On the other hand, in a statement like
 501     // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
 502     // DefMap maps <ty> to `id` instead.
 503     fn symbol_is_live(&mut self,
 504                       id: ast::NodeId,
 505                       ctor_id: Option<ast::NodeId>)
 506                       -> bool {
 507         if self.live_symbols.contains(&id)
 508            || ctor_id.map_or(false,
 509                              |ctor| self.live_symbols.contains(&ctor)) {
 510             return true;
 511         }
 512         // If it's a type whose items are live, then it's live, too.
 513         // This is done to handle the case where, for example, the static
 514         // method of a private type is used, but the type itself is never
 515         // called directly.
 516         let def_id = self.tcx.hir.local_def_id(id);
 517         let inherent_impls = self.tcx.inherent_impls(def_id);
 518         for &impl_did in inherent_impls.iter() {
 519             for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
 520                 if let Some(item_node_id) = self.tcx.hir.as_local_node_id(item_did) {
 521                     if self.live_symbols.contains(&item_node_id) {
 522                         return true;
 523                     }
 524                 }
 525             }
 526         }
 527         false
 528     }
 529
 530     fn warn_dead_code(&mut self,
 531                       id: ast::NodeId,
 532                       span: syntax_pos::Span,
 533                       name: ast::Name,
 534                       node_type: &str,
 535                       participle: &str) {
 536         if !name.as_str().starts_with("_") {
 537             self.tcx
 538                 .lint_node(lint::builtin::DEAD_CODE,
 539                            id,
 540                            span,
 541                            &format!("{} is never {}: `{}`",
 542                                     node_type, participle, name));
 543         }
 544     }
 545 }
 546
 547 impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
 548     /// Walk nested items in place so that we don't report dead-code
 549     /// on inner functions when the outer function is already getting
 550     /// an error. We could do this also by checking the parents, but
 551     /// this is how the code is setup and it seems harmless enough.
 552     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 553         NestedVisitorMap::All(&self.tcx.hir)
 554     }
 555
 556     fn visit_item(&mut self, item: &'tcx hir::Item) {
 557         if self.should_warn_about_item(item) {
 558             // For items that have a definition with a signature followed by a
 559             // block, point only at the signature.
 560             let span = match item.node {
 561                 hir::ItemFn(..) |
 562                 hir::ItemMod(..) |
 563                 hir::ItemEnum(..) |
 564                 hir::ItemStruct(..) |
 565                 hir::ItemUnion(..) |
 566                 hir::ItemTrait(..) |
 567                 hir::ItemAutoImpl(..) |
 568                 hir::ItemImpl(..) => self.tcx.sess.codemap().def_span(item.span),
 569                 _ => item.span,
 570             };
 571             self.warn_dead_code(
 572                 item.id,
 573                 span,
 574                 item.name,
 575                 item.node.descriptive_variant(),
 576                 "used",
 577             );
 578         } else {
 579             // Only continue if we didn't warn
 580             intravisit::walk_item(self, item);
 581         }
 582     }
 583
 584     fn visit_variant(&mut self,
 585                      variant: &'tcx hir::Variant,
 586                      g: &'tcx hir::Generics,
 587                      id: ast::NodeId) {
 588         if self.should_warn_about_variant(&variant.node) {
 589             self.warn_dead_code(variant.node.data.id(), variant.span, variant.node.name,
 590                                 "variant", "constructed");
 591         } else {
 592             intravisit::walk_variant(self, variant, g, id);
 593         }
 594     }
 595
 596     fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem) {
 597         if self.should_warn_about_foreign_item(fi) {
 598             self.warn_dead_code(fi.id, fi.span, fi.name,
 599                                 fi.node.descriptive_variant(), "used");
 600         }
 601         intravisit::walk_foreign_item(self, fi);
 602     }
 603
 604     fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
 605         if self.should_warn_about_field(&field) {
 606             self.warn_dead_code(field.id, field.span, field.name, "field", "used");
 607         }
 608         intravisit::walk_struct_field(self, field);
 609     }
 610
 611     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
 612         match impl_item.node {
 613             hir::ImplItemKind::Const(_, body_id) => {
 614                 if !self.symbol_is_live(impl_item.id, None) {
 615                     self.warn_dead_code(impl_item.id,
 616                                         impl_item.span,
 617                                         impl_item.name,
 618                                         "associated const",
 619                                         "used");
 620                 }
 621                 self.visit_nested_body(body_id)
 622             }
 623             hir::ImplItemKind::Method(_, body_id) => {
 624                 if !self.symbol_is_live(impl_item.id, None) {
 625                     let span = self.tcx.sess.codemap().def_span(impl_item.span);
 626                     self.warn_dead_code(impl_item.id, span, impl_item.name, "method", "used");
 627                 }
 628                 self.visit_nested_body(body_id)
 629             }
 630             hir::ImplItemKind::Type(..) => {}
 631         }
 632     }
 633
 634     // Overwrite so that we don't warn the trait item itself.
 635     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
 636         match trait_item.node {
 637             hir::TraitItemKind::Const(_, Some(body_id)) |
 638             hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
 639                 self.visit_nested_body(body_id)
 640             }
 641             hir::TraitItemKind::Const(_, None) |
 642             hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) |
 643             hir::TraitItemKind::Type(..) => {}
 644         }
 645     }
 646 }
 647
 648 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 649     let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
 650     let krate = tcx.hir.krate();
 651     let live_symbols = find_live(tcx, access_levels, krate);
 652     let mut visitor = DeadVisitor {
 653         tcx,
 654         live_symbols,
 655     };
 656     intravisit::walk_crate(&mut visitor, krate);
 657 }