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 middle::{def, pat_util, privacy, ty};
  16 use lint;
  17 use util::nodemap::NodeSet;
  18
  19 use std::collections::HashSet;
  20 use syntax::{ast, ast_map, codemap};
  21 use syntax::ast_util::{local_def, is_local};
  22 use syntax::attr::{self, AttrMetaMethods};
  23 use syntax::visit::{self, Visitor};
  24
  25 // Any local node that may call something in its body block should be
  26 // explored. For example, if it's a live NodeItem that is a
  27 // function, then we should explore its block to check for codes that
  28 // may need to be marked as live.
  29 fn should_explore(tcx: &ty::ctxt, def_id: ast::DefId) -> bool {
  30     if !is_local(def_id) {
  31         return false;
  32     }
  33
  34     match tcx.map.find(def_id.node) {
  35         Some(ast_map::NodeItem(..))
  36         | Some(ast_map::NodeImplItem(..))
  37         | Some(ast_map::NodeForeignItem(..))
  38         | Some(ast_map::NodeTraitItem(..)) => true,
  39         _ => false
  40     }
  41 }
  42
  43 struct MarkSymbolVisitor<'a, 'tcx: 'a> {
  44     worklist: Vec<ast::NodeId>,
  45     tcx: &'a ty::ctxt<'tcx>,
  46     live_symbols: Box<HashSet<ast::NodeId>>,
  47     struct_has_extern_repr: bool,
  48     ignore_non_const_paths: bool,
  49     inherited_pub_visibility: bool,
  50 }
  51
  52 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
  53     fn new(tcx: &'a ty::ctxt<'tcx>,
  54            worklist: Vec<ast::NodeId>) -> MarkSymbolVisitor<'a, 'tcx> {
  55         MarkSymbolVisitor {
  56             worklist: worklist,
  57             tcx: tcx,
  58             live_symbols: box HashSet::new(),
  59             struct_has_extern_repr: false,
  60             ignore_non_const_paths: false,
  61             inherited_pub_visibility: false,
  62         }
  63     }
  64
  65     fn check_def_id(&mut self, def_id: ast::DefId) {
  66         if should_explore(self.tcx, def_id) {
  67             self.worklist.push(def_id.node);
  68         }
  69         self.live_symbols.insert(def_id.node);
  70     }
  71
  72     fn lookup_and_handle_definition(&mut self, id: &ast::NodeId) {
  73         self.tcx.def_map.borrow().get(id).map(|def| {
  74             match def.full_def() {
  75                 def::DefConst(_) => {
  76                     self.check_def_id(def.def_id())
  77                 }
  78                 _ if self.ignore_non_const_paths => (),
  79                 def::DefPrimTy(_) => (),
  80                 def::DefVariant(enum_id, variant_id, _) => {
  81                     self.check_def_id(enum_id);
  82                     self.check_def_id(variant_id);
  83                 }
  84                 _ => {
  85                     self.check_def_id(def.def_id());
  86                 }
  87             }
  88         });
  89     }
  90
  91     fn lookup_and_handle_method(&mut self, id: ast::NodeId,
  92                                 span: codemap::Span) {
  93         let method_call = ty::MethodCall::expr(id);
  94         match self.tcx.method_map.borrow().get(&method_call) {
  95             Some(method) => {
  96                 match method.origin {
  97                     ty::MethodStatic(def_id) => {
  98                         match ty::provided_source(self.tcx, def_id) {
  99                             Some(p_did) => self.check_def_id(p_did),
 100                             None => self.check_def_id(def_id)
 101                         }
 102                     }
 103                     ty::MethodStaticClosure(_) => {}
 104                     ty::MethodTypeParam(ty::MethodParam {
 105                         ref trait_ref,
 106                         method_num: index,
 107                         ..
 108                     }) |
 109                     ty::MethodTraitObject(ty::MethodObject {
 110                         ref trait_ref,
 111                         method_num: index,
 112                         ..
 113                     }) => {
 114                         let trait_item = ty::trait_item(self.tcx,
 115                                                         trait_ref.def_id,
 116                                                         index);
 117                         match trait_item {
 118                             ty::MethodTraitItem(method) => {
 119                                 self.check_def_id(method.def_id);
 120                             }
 121                             ty::TypeTraitItem(typedef) => {
 122                                 self.check_def_id(typedef.def_id);
 123                             }
 124                         }
 125                     }
 126                 }
 127             }
 128             None => {
 129                 self.tcx.sess.span_bug(span,
 130                                        "method call expression not \
 131                                         in method map?!")
 132             }
 133         }
 134     }
 135
 136     fn handle_field_access(&mut self, lhs: &ast::Expr, name: &ast::Ident) {
 137         match ty::expr_ty_adjusted(self.tcx, lhs).sty {
 138             ty::ty_struct(id, _) => {
 139                 let fields = ty::lookup_struct_fields(self.tcx, id);
 140                 let field_id = fields.iter()
 141                     .find(|field| field.name == name.name).unwrap().id;
 142                 self.live_symbols.insert(field_id.node);
 143             },
 144             _ => ()
 145         }
 146     }
 147
 148     fn handle_tup_field_access(&mut self, lhs: &ast::Expr, idx: usize) {
 149         match ty::expr_ty_adjusted(self.tcx, lhs).sty {
 150             ty::ty_struct(id, _) => {
 151                 let fields = ty::lookup_struct_fields(self.tcx, id);
 152                 let field_id = fields[idx].id;
 153                 self.live_symbols.insert(field_id.node);
 154             },
 155             _ => ()
 156         }
 157     }
 158
 159     fn handle_field_pattern_match(&mut self, lhs: &ast::Pat,
 160                                   pats: &[codemap::Spanned<ast::FieldPat>]) {
 161         let id = match self.tcx.def_map.borrow().get(&lhs.id).unwrap().full_def() {
 162             def::DefVariant(_, id, _) => id,
 163             _ => {
 164                 match ty::ty_to_def_id(ty::node_id_to_type(self.tcx,
 165                                                            lhs.id)) {
 166                     None => {
 167                         self.tcx.sess.span_bug(lhs.span,
 168                                                "struct pattern wasn't of a \
 169                                                 type with a def ID?!")
 170                     }
 171                     Some(def_id) => def_id,
 172                 }
 173             }
 174         };
 175         let fields = ty::lookup_struct_fields(self.tcx, id);
 176         for pat in pats {
 177             let field_id = fields.iter()
 178                 .find(|field| field.name == pat.node.ident.name).unwrap().id;
 179             self.live_symbols.insert(field_id.node);
 180         }
 181     }
 182
 183     fn mark_live_symbols(&mut self) {
 184         let mut scanned = HashSet::new();
 185         while self.worklist.len() > 0 {
 186             let id = self.worklist.pop().unwrap();
 187             if scanned.contains(&id) {
 188                 continue
 189             }
 190             scanned.insert(id);
 191
 192             match self.tcx.map.find(id) {
 193                 Some(ref node) => {
 194                     self.live_symbols.insert(id);
 195                     self.visit_node(node);
 196                 }
 197                 None => (),
 198             }
 199         }
 200     }
 201
 202     fn visit_node(&mut self, node: &ast_map::Node) {
 203         let had_extern_repr = self.struct_has_extern_repr;
 204         self.struct_has_extern_repr = false;
 205         let had_inherited_pub_visibility = self.inherited_pub_visibility;
 206         self.inherited_pub_visibility = false;
 207         match *node {
 208             ast_map::NodeItem(item) => {
 209                 match item.node {
 210                     ast::ItemStruct(..) => {
 211                         self.struct_has_extern_repr = item.attrs.iter().any(|attr| {
 212                             attr::find_repr_attrs(self.tcx.sess.diagnostic(), attr)
 213                                 .contains(&attr::ReprExtern)
 214                         });
 215
 216                         visit::walk_item(self, &*item);
 217                     }
 218                     ast::ItemEnum(..) => {
 219                         self.inherited_pub_visibility = item.vis == ast::Public;
 220                         visit::walk_item(self, &*item);
 221                     }
 222                     ast::ItemFn(..)
 223                     | ast::ItemTy(..)
 224                     | ast::ItemStatic(..)
 225                     | ast::ItemConst(..) => {
 226                         visit::walk_item(self, &*item);
 227                     }
 228                     _ => ()
 229                 }
 230             }
 231             ast_map::NodeTraitItem(trait_item) => {
 232                 visit::walk_trait_item(self, trait_item);
 233             }
 234             ast_map::NodeImplItem(impl_item) => {
 235                 visit::walk_impl_item(self, impl_item);
 236             }
 237             ast_map::NodeForeignItem(foreign_item) => {
 238                 visit::walk_foreign_item(self, &*foreign_item);
 239             }
 240             _ => ()
 241         }
 242         self.struct_has_extern_repr = had_extern_repr;
 243         self.inherited_pub_visibility = had_inherited_pub_visibility;
 244     }
 245 }
 246
 247 impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
 248
 249     fn visit_struct_def(&mut self, def: &ast::StructDef, _: ast::Ident,
 250                         _: &ast::Generics, _: ast::NodeId) {
 251         let has_extern_repr = self.struct_has_extern_repr;
 252         let inherited_pub_visibility = self.inherited_pub_visibility;
 253         let live_fields = def.fields.iter().filter(|f| {
 254             has_extern_repr || inherited_pub_visibility || match f.node.kind {
 255                 ast::NamedField(_, ast::Public) => true,
 256                 _ => false
 257             }
 258         });
 259         self.live_symbols.extend(live_fields.map(|f| f.node.id));
 260
 261         visit::walk_struct_def(self, def);
 262     }
 263
 264     fn visit_expr(&mut self, expr: &ast::Expr) {
 265         match expr.node {
 266             ast::ExprMethodCall(..) => {
 267                 self.lookup_and_handle_method(expr.id, expr.span);
 268             }
 269             ast::ExprField(ref lhs, ref ident) => {
 270                 self.handle_field_access(&**lhs, &ident.node);
 271             }
 272             ast::ExprTupField(ref lhs, idx) => {
 273                 self.handle_tup_field_access(&**lhs, idx.node);
 274             }
 275             _ => ()
 276         }
 277
 278         visit::walk_expr(self, expr);
 279     }
 280
 281     fn visit_pat(&mut self, pat: &ast::Pat) {
 282         let def_map = &self.tcx.def_map;
 283         match pat.node {
 284             ast::PatStruct(_, ref fields, _) => {
 285                 self.handle_field_pattern_match(pat, fields);
 286             }
 287             _ if pat_util::pat_is_const(def_map, pat) => {
 288                 // it might be the only use of a const
 289                 self.lookup_and_handle_definition(&pat.id)
 290             }
 291             _ => ()
 292         }
 293
 294         self.ignore_non_const_paths = true;
 295         visit::walk_pat(self, pat);
 296         self.ignore_non_const_paths = false;
 297     }
 298
 299     fn visit_path(&mut self, path: &ast::Path, id: ast::NodeId) {
 300         self.lookup_and_handle_definition(&id);
 301         visit::walk_path(self, path);
 302     }
 303
 304     fn visit_item(&mut self, _: &ast::Item) {
 305         // Do not recurse into items. These items will be added to the
 306         // worklist and recursed into manually if necessary.
 307     }
 308 }
 309
 310 fn has_allow_dead_code_or_lang_attr(attrs: &[ast::Attribute]) -> bool {
 311     if attr::contains_name(attrs, "lang") {
 312         return true;
 313     }
 314
 315     let dead_code = lint::builtin::DEAD_CODE.name_lower();
 316     for attr in lint::gather_attrs(attrs) {
 317         match attr {
 318             Ok((ref name, lint::Allow, _))
 319                 if &name[..] == dead_code => return true,
 320             _ => (),
 321         }
 322     }
 323     false
 324 }
 325
 326 // This visitor seeds items that
 327 //   1) We want to explicitly consider as live:
 328 //     * Item annotated with #[allow(dead_code)]
 329 //         - This is done so that if we want to suppress warnings for a
 330 //           group of dead functions, we only have to annotate the "root".
 331 //           For example, if both `f` and `g` are dead and `f` calls `g`,
 332 //           then annotating `f` with `#[allow(dead_code)]` will suppress
 333 //           warning for both `f` and `g`.
 334 //     * Item annotated with #[lang=".."]
 335 //         - This is because lang items are always callable from elsewhere.
 336 //   or
 337 //   2) We are not sure to be live or not
 338 //     * Implementation of a trait method
 339 struct LifeSeeder {
 340     worklist: Vec<ast::NodeId>
 341 }
 342
 343 impl<'v> Visitor<'v> for LifeSeeder {
 344     fn visit_item(&mut self, item: &ast::Item) {
 345         let allow_dead_code = has_allow_dead_code_or_lang_attr(&item.attrs);
 346         if allow_dead_code {
 347             self.worklist.push(item.id);
 348         }
 349         match item.node {
 350             ast::ItemEnum(ref enum_def, _) if allow_dead_code => {
 351                 self.worklist.extend(enum_def.variants.iter().map(|variant| variant.node.id));
 352             }
 353             ast::ItemTrait(_, _, _, ref trait_items) => {
 354                 for trait_item in trait_items {
 355                     match trait_item.node {
 356                         ast::MethodTraitItem(_, Some(_)) => {
 357                             if has_allow_dead_code_or_lang_attr(&trait_item.attrs) {
 358                                 self.worklist.push(trait_item.id);
 359                             }
 360                         }
 361                         _ => {}
 362                     }
 363                 }
 364             }
 365             ast::ItemImpl(_, _, _, ref opt_trait, _, ref impl_items) => {
 366                 for impl_item in impl_items {
 367                     match impl_item.node {
 368                         ast::MethodImplItem(..) => {
 369                             if opt_trait.is_some() ||
 370                                     has_allow_dead_code_or_lang_attr(&impl_item.attrs) {
 371                                 self.worklist.push(impl_item.id);
 372                             }
 373                         }
 374                         ast::TypeImplItem(_) => {}
 375                         ast::MacImplItem(_) => panic!("unexpanded macro")
 376                     }
 377                 }
 378             }
 379             _ => ()
 380         }
 381         visit::walk_item(self, item);
 382     }
 383 }
 384
 385 fn create_and_seed_worklist(tcx: &ty::ctxt,
 386                             exported_items: &privacy::ExportedItems,
 387                             reachable_symbols: &NodeSet,
 388                             krate: &ast::Crate) -> Vec<ast::NodeId> {
 389     let mut worklist = Vec::new();
 390
 391     // Preferably, we would only need to seed the worklist with reachable
 392     // symbols. However, since the set of reachable symbols differs
 393     // depending on whether a crate is built as bin or lib, and we want
 394     // the warning to be consistent, we also seed the worklist with
 395     // exported symbols.
 396     for id in exported_items {
 397         worklist.push(*id);
 398     }
 399     for id in reachable_symbols {
 400         worklist.push(*id);
 401     }
 402
 403     // Seed entry point
 404     match *tcx.sess.entry_fn.borrow() {
 405         Some((id, _)) => worklist.push(id),
 406         None => ()
 407     }
 408
 409     // Seed implemented trait methods
 410     let mut life_seeder = LifeSeeder {
 411         worklist: worklist
 412     };
 413     visit::walk_crate(&mut life_seeder, krate);
 414
 415     return life_seeder.worklist;
 416 }
 417
 418 fn find_live(tcx: &ty::ctxt,
 419              exported_items: &privacy::ExportedItems,
 420              reachable_symbols: &NodeSet,
 421              krate: &ast::Crate)
 422              -> Box<HashSet<ast::NodeId>> {
 423     let worklist = create_and_seed_worklist(tcx, exported_items,
 424                                             reachable_symbols, krate);
 425     let mut symbol_visitor = MarkSymbolVisitor::new(tcx, worklist);
 426     symbol_visitor.mark_live_symbols();
 427     symbol_visitor.live_symbols
 428 }
 429
 430 fn get_struct_ctor_id(item: &ast::Item) -> Option<ast::NodeId> {
 431     match item.node {
 432         ast::ItemStruct(ref struct_def, _) => struct_def.ctor_id,
 433         _ => None
 434     }
 435 }
 436
 437 struct DeadVisitor<'a, 'tcx: 'a> {
 438     tcx: &'a ty::ctxt<'tcx>,
 439     live_symbols: Box<HashSet<ast::NodeId>>,
 440 }
 441
 442 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
 443     fn should_warn_about_item(&mut self, item: &ast::Item) -> bool {
 444         let should_warn = match item.node {
 445             ast::ItemStatic(..)
 446             | ast::ItemConst(..)
 447             | ast::ItemFn(..)
 448             | ast::ItemEnum(..)
 449             | ast::ItemStruct(..) => true,
 450             _ => false
 451         };
 452         let ctor_id = get_struct_ctor_id(item);
 453         should_warn && !self.symbol_is_live(item.id, ctor_id)
 454     }
 455
 456     fn should_warn_about_field(&mut self, node: &ast::StructField_) -> bool {
 457         let is_named = node.ident().is_some();
 458         let field_type = ty::node_id_to_type(self.tcx, node.id);
 459         let is_marker_field = match ty::ty_to_def_id(field_type) {
 460             Some(def_id) => self.tcx.lang_items.items().any(|(_, item)| *item == Some(def_id)),
 461             _ => false
 462         };
 463         is_named
 464             && !self.symbol_is_live(node.id, None)
 465             && !is_marker_field
 466             && !has_allow_dead_code_or_lang_attr(&node.attrs)
 467     }
 468
 469     fn should_warn_about_variant(&mut self, variant: &ast::Variant_) -> bool {
 470         !self.symbol_is_live(variant.id, None)
 471             && !has_allow_dead_code_or_lang_attr(&variant.attrs)
 472     }
 473
 474     // id := node id of an item's definition.
 475     // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
 476     //            `None` otherwise.
 477     // If the item is a struct_ctor, then either its `id` or
 478     // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
 479     // DefMap maps the ExprPath of a struct_ctor to the node referred by
 480     // `ctor_id`. On the other hand, in a statement like
 481     // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
 482     // DefMap maps <ty> to `id` instead.
 483     fn symbol_is_live(&mut self, id: ast::NodeId,
 484                       ctor_id: Option<ast::NodeId>) -> bool {
 485         if self.live_symbols.contains(&id)
 486            || ctor_id.map_or(false,
 487                              |ctor| self.live_symbols.contains(&ctor)) {
 488             return true;
 489         }
 490         // If it's a type whose methods are live, then it's live, too.
 491         // This is done to handle the case where, for example, the static
 492         // method of a private type is used, but the type itself is never
 493         // called directly.
 494         let impl_items = self.tcx.impl_items.borrow();
 495         match self.tcx.inherent_impls.borrow().get(&local_def(id)) {
 496             None => (),
 497             Some(impl_list) => {
 498                 for impl_did in &**impl_list {
 499                     for item_did in &*impl_items.get(impl_did).unwrap() {
 500                         if self.live_symbols.contains(&item_did.def_id()
 501                                                                .node) {
 502                             return true;
 503                         }
 504                     }
 505                 }
 506             }
 507         }
 508         false
 509     }
 510
 511     fn warn_dead_code(&mut self,
 512                       id: ast::NodeId,
 513                       span: codemap::Span,
 514                       ident: ast::Ident,
 515                       node_type: &str) {
 516         let name = ident.as_str();
 517         if !name.starts_with("_") {
 518             self.tcx
 519                 .sess
 520                 .add_lint(lint::builtin::DEAD_CODE,
 521                           id,
 522                           span,
 523                           format!("{} is never used: `{}`", node_type, name));
 524         }
 525     }
 526 }
 527
 528 impl<'a, 'tcx, 'v> Visitor<'v> for DeadVisitor<'a, 'tcx> {
 529     fn visit_item(&mut self, item: &ast::Item) {
 530         if self.should_warn_about_item(item) {
 531             self.warn_dead_code(item.id, item.span, item.ident, item.node.descriptive_variant());
 532         } else {
 533             match item.node {
 534                 ast::ItemEnum(ref enum_def, _) => {
 535                     for variant in &enum_def.variants {
 536                         if self.should_warn_about_variant(&variant.node) {
 537                             self.warn_dead_code(variant.node.id, variant.span,
 538                                                 variant.node.name, "variant");
 539                         }
 540                     }
 541                 },
 542                 _ => ()
 543             }
 544         }
 545         visit::walk_item(self, item);
 546     }
 547
 548     fn visit_foreign_item(&mut self, fi: &ast::ForeignItem) {
 549         if !self.symbol_is_live(fi.id, None) {
 550             self.warn_dead_code(fi.id, fi.span, fi.ident, fi.node.descriptive_variant());
 551         }
 552         visit::walk_foreign_item(self, fi);
 553     }
 554
 555     fn visit_fn(&mut self, fk: visit::FnKind<'v>,
 556                 _: &'v ast::FnDecl, block: &'v ast::Block,
 557                 span: codemap::Span, id: ast::NodeId) {
 558         // Have to warn method here because methods are not ast::Item
 559         match fk {
 560             visit::FkMethod(name, _) => {
 561                 if !self.symbol_is_live(id, None) {
 562                     self.warn_dead_code(id, span, name, "method");
 563                 }
 564             }
 565             _ => ()
 566         }
 567         visit::walk_block(self, block);
 568     }
 569
 570     fn visit_struct_field(&mut self, field: &ast::StructField) {
 571         if self.should_warn_about_field(&field.node) {
 572             self.warn_dead_code(field.node.id, field.span,
 573                                 field.node.ident().unwrap(), "struct field");
 574         }
 575
 576         visit::walk_struct_field(self, field);
 577     }
 578
 579     // Overwrite so that we don't warn the trait method itself.
 580     fn visit_trait_item(&mut self, trait_method: &ast::TraitItem) {
 581         match trait_method.node {
 582             ast::MethodTraitItem(_, Some(ref body)) => {
 583                 visit::walk_block(self, body)
 584             }
 585             ast::MethodTraitItem(_, None) |
 586             ast::TypeTraitItem(..) => {}
 587         }
 588     }
 589 }
 590
 591 pub fn check_crate(tcx: &ty::ctxt,
 592                    exported_items: &privacy::ExportedItems,
 593                    reachable_symbols: &NodeSet) {
 594     let krate = tcx.map.krate();
 595     let live_symbols = find_live(tcx, exported_items,
 596                                  reachable_symbols, krate);
 597     let mut visitor = DeadVisitor { tcx: tcx, live_symbols: live_symbols };
 598     visit::walk_crate(&mut visitor, krate);
 599 }