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.
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.
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.
15 use front::map as ast_map;
17 use rustc_front::visit::{self, Visitor};
19 use middle::{def, pat_util, privacy, ty};
20 use middle::def_id::{DefId};
22 use util::nodemap::NodeSet;
24 use std::collections::HashSet;
25 use syntax::{ast, codemap};
26 use syntax::attr::{self, AttrMetaMethods};
28 // Any local node that may call something in its body block should be
29 // explored. For example, if it's a live NodeItem that is a
30 // function, then we should explore its block to check for codes that
31 // may need to be marked as live.
32 fn should_explore(tcx: &ty::ctxt, node_id: ast::NodeId) -> bool {
33 match tcx.map.find(node_id) {
34 Some(ast_map::NodeItem(..)) |
35 Some(ast_map::NodeImplItem(..)) |
36 Some(ast_map::NodeForeignItem(..)) |
37 Some(ast_map::NodeTraitItem(..)) =>
44 struct MarkSymbolVisitor<'a, 'tcx: 'a> {
45 worklist: Vec<ast::NodeId>,
46 tcx: &'a ty::ctxt<'tcx>,
47 live_symbols: Box<HashSet<ast::NodeId>>,
48 struct_has_extern_repr: bool,
49 ignore_non_const_paths: bool,
50 inherited_pub_visibility: bool,
51 ignore_variant_stack: Vec<DefId>,
54 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
55 fn new(tcx: &'a ty::ctxt<'tcx>,
56 worklist: Vec<ast::NodeId>) -> MarkSymbolVisitor<'a, 'tcx> {
60 live_symbols: box HashSet::new(),
61 struct_has_extern_repr: false,
62 ignore_non_const_paths: false,
63 inherited_pub_visibility: false,
64 ignore_variant_stack: vec![],
68 fn check_def_id(&mut self, def_id: DefId) {
69 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
70 if should_explore(self.tcx, node_id) {
71 self.worklist.push(node_id);
73 self.live_symbols.insert(node_id);
77 fn insert_def_id(&mut self, def_id: DefId) {
78 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
79 debug_assert!(!should_explore(self.tcx, node_id));
80 self.live_symbols.insert(node_id);
84 fn lookup_and_handle_definition(&mut self, id: &ast::NodeId) {
85 use middle::ty::TypeVariants::{TyEnum, TyStruct};
87 // If `bar` is a trait item, make sure to mark Foo as alive in `Foo::bar`
88 self.tcx.tables.borrow().item_substs.get(id)
89 .and_then(|substs| substs.substs.self_ty())
90 .map(|ty| match ty.sty {
91 TyEnum(tyid, _) | TyStruct(tyid, _) => self.check_def_id(tyid.did),
95 self.tcx.def_map.borrow().get(id).map(|def| {
96 match def.full_def() {
97 def::DefConst(_) | def::DefAssociatedConst(..) => {
98 self.check_def_id(def.def_id());
100 _ if self.ignore_non_const_paths => (),
101 def::DefPrimTy(_) => (),
102 def::DefSelfTy(..) => (),
103 def::DefVariant(enum_id, variant_id, _) => {
104 self.check_def_id(enum_id);
105 if !self.ignore_variant_stack.contains(&variant_id) {
106 self.check_def_id(variant_id);
110 self.check_def_id(def.def_id());
116 fn lookup_and_handle_method(&mut self, id: ast::NodeId) {
117 let method_call = ty::MethodCall::expr(id);
118 let method = self.tcx.tables.borrow().method_map[&method_call];
119 self.check_def_id(method.def_id);
122 fn handle_field_access(&mut self, lhs: &hir::Expr, name: ast::Name) {
123 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
124 self.insert_def_id(def.struct_variant().field_named(name).did);
126 self.tcx.sess.span_bug(lhs.span, "named field access on non-struct")
130 fn handle_tup_field_access(&mut self, lhs: &hir::Expr, idx: usize) {
131 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
132 self.insert_def_id(def.struct_variant().fields[idx].did);
136 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat,
137 pats: &[codemap::Spanned<hir::FieldPat>]) {
138 let def = self.tcx.def_map.borrow().get(&lhs.id).unwrap().full_def();
139 let pat_ty = self.tcx.node_id_to_type(lhs.id);
140 let variant = match pat_ty.sty {
141 ty::TyStruct(adt, _) | ty::TyEnum(adt, _) => adt.variant_of_def(def),
142 _ => self.tcx.sess.span_bug(lhs.span, "non-ADT in struct pattern")
145 if let hir::PatWild(hir::PatWildSingle) = pat.node.pat.node {
148 self.insert_def_id(variant.field_named(pat.node.name).did);
152 fn mark_live_symbols(&mut self) {
153 let mut scanned = HashSet::new();
154 while !self.worklist.is_empty() {
155 let id = self.worklist.pop().unwrap();
156 if scanned.contains(&id) {
161 match self.tcx.map.find(id) {
163 self.live_symbols.insert(id);
164 self.visit_node(node);
171 fn visit_node(&mut self, node: &ast_map::Node) {
172 let had_extern_repr = self.struct_has_extern_repr;
173 self.struct_has_extern_repr = false;
174 let had_inherited_pub_visibility = self.inherited_pub_visibility;
175 self.inherited_pub_visibility = false;
177 ast_map::NodeItem(item) => {
179 hir::ItemStruct(..) => {
180 self.struct_has_extern_repr = item.attrs.iter().any(|attr| {
181 attr::find_repr_attrs(self.tcx.sess.diagnostic(), attr)
182 .contains(&attr::ReprExtern)
185 visit::walk_item(self, &*item);
187 hir::ItemEnum(..) => {
188 self.inherited_pub_visibility = item.vis == hir::Public;
189 visit::walk_item(self, &*item);
193 | hir::ItemStatic(..)
194 | hir::ItemConst(..) => {
195 visit::walk_item(self, &*item);
200 ast_map::NodeTraitItem(trait_item) => {
201 visit::walk_trait_item(self, trait_item);
203 ast_map::NodeImplItem(impl_item) => {
204 visit::walk_impl_item(self, impl_item);
206 ast_map::NodeForeignItem(foreign_item) => {
207 visit::walk_foreign_item(self, &*foreign_item);
211 self.struct_has_extern_repr = had_extern_repr;
212 self.inherited_pub_visibility = had_inherited_pub_visibility;
216 impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
218 fn visit_struct_def(&mut self, def: &hir::StructDef, _: ast::Name,
219 _: &hir::Generics, _: ast::NodeId) {
220 let has_extern_repr = self.struct_has_extern_repr;
221 let inherited_pub_visibility = self.inherited_pub_visibility;
222 let live_fields = def.fields.iter().filter(|f| {
223 has_extern_repr || inherited_pub_visibility || match f.node.kind {
224 hir::NamedField(_, hir::Public) => true,
228 self.live_symbols.extend(live_fields.map(|f| f.node.id));
230 visit::walk_struct_def(self, def);
233 fn visit_expr(&mut self, expr: &hir::Expr) {
235 hir::ExprMethodCall(..) => {
236 self.lookup_and_handle_method(expr.id);
238 hir::ExprField(ref lhs, ref name) => {
239 self.handle_field_access(&**lhs, name.node);
241 hir::ExprTupField(ref lhs, idx) => {
242 self.handle_tup_field_access(&**lhs, idx.node);
247 visit::walk_expr(self, expr);
250 fn visit_arm(&mut self, arm: &hir::Arm) {
251 if arm.pats.len() == 1 {
252 let pat = &*arm.pats[0];
253 let variants = pat_util::necessary_variants(&self.tcx.def_map, pat);
255 // Inside the body, ignore constructions of variants
256 // necessary for the pattern to match. Those construction sites
257 // can't be reached unless the variant is constructed elsewhere.
258 let len = self.ignore_variant_stack.len();
259 self.ignore_variant_stack.push_all(&*variants);
260 visit::walk_arm(self, arm);
261 self.ignore_variant_stack.truncate(len);
263 visit::walk_arm(self, arm);
267 fn visit_pat(&mut self, pat: &hir::Pat) {
268 let def_map = &self.tcx.def_map;
270 hir::PatStruct(_, ref fields, _) => {
271 self.handle_field_pattern_match(pat, fields);
273 _ if pat_util::pat_is_const(def_map, pat) => {
274 // it might be the only use of a const
275 self.lookup_and_handle_definition(&pat.id)
280 self.ignore_non_const_paths = true;
281 visit::walk_pat(self, pat);
282 self.ignore_non_const_paths = false;
285 fn visit_path(&mut self, path: &hir::Path, id: ast::NodeId) {
286 self.lookup_and_handle_definition(&id);
287 visit::walk_path(self, path);
290 fn visit_path_list_item(&mut self, path: &hir::Path, item: &hir::PathListItem) {
291 self.lookup_and_handle_definition(&item.node.id());
292 visit::walk_path_list_item(self, path, item);
295 fn visit_item(&mut self, _: &hir::Item) {
296 // Do not recurse into items. These items will be added to the
297 // worklist and recursed into manually if necessary.
301 fn has_allow_dead_code_or_lang_attr(attrs: &[ast::Attribute]) -> bool {
302 if attr::contains_name(attrs, "lang") {
306 let dead_code = lint::builtin::DEAD_CODE.name_lower();
307 for attr in lint::gather_attrs(attrs) {
309 Ok((ref name, lint::Allow, _))
310 if &name[..] == dead_code => return true,
317 // This visitor seeds items that
318 // 1) We want to explicitly consider as live:
319 // * Item annotated with #[allow(dead_code)]
320 // - This is done so that if we want to suppress warnings for a
321 // group of dead functions, we only have to annotate the "root".
322 // For example, if both `f` and `g` are dead and `f` calls `g`,
323 // then annotating `f` with `#[allow(dead_code)]` will suppress
324 // warning for both `f` and `g`.
325 // * Item annotated with #[lang=".."]
326 // - This is because lang items are always callable from elsewhere.
328 // 2) We are not sure to be live or not
329 // * Implementation of a trait method
331 worklist: Vec<ast::NodeId>
334 impl<'v> Visitor<'v> for LifeSeeder {
335 fn visit_item(&mut self, item: &hir::Item) {
336 let allow_dead_code = has_allow_dead_code_or_lang_attr(&item.attrs);
338 self.worklist.push(item.id);
341 hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
342 self.worklist.extend(enum_def.variants.iter().map(|variant| variant.node.id));
344 hir::ItemTrait(_, _, _, ref trait_items) => {
345 for trait_item in trait_items {
346 match trait_item.node {
347 hir::ConstTraitItem(_, Some(_)) |
348 hir::MethodTraitItem(_, Some(_)) => {
349 if has_allow_dead_code_or_lang_attr(&trait_item.attrs) {
350 self.worklist.push(trait_item.id);
357 hir::ItemImpl(_, _, _, ref opt_trait, _, ref impl_items) => {
358 for impl_item in impl_items {
359 match impl_item.node {
360 hir::ConstImplItem(..) |
361 hir::MethodImplItem(..) => {
362 if opt_trait.is_some() ||
363 has_allow_dead_code_or_lang_attr(&impl_item.attrs) {
364 self.worklist.push(impl_item.id);
367 hir::TypeImplItem(_) => {}
373 visit::walk_item(self, item);
377 fn create_and_seed_worklist(tcx: &ty::ctxt,
378 exported_items: &privacy::ExportedItems,
379 reachable_symbols: &NodeSet,
380 krate: &hir::Crate) -> Vec<ast::NodeId> {
381 let mut worklist = Vec::new();
383 // Preferably, we would only need to seed the worklist with reachable
384 // symbols. However, since the set of reachable symbols differs
385 // depending on whether a crate is built as bin or lib, and we want
386 // the warning to be consistent, we also seed the worklist with
388 for id in exported_items {
391 for id in reachable_symbols {
392 // Reachable variants can be dead, because we warn about
393 // variants never constructed, not variants never used.
394 if let Some(ast_map::NodeVariant(..)) = tcx.map.find(*id) {
401 match *tcx.sess.entry_fn.borrow() {
402 Some((id, _)) => worklist.push(id),
406 // Seed implemented trait items
407 let mut life_seeder = LifeSeeder {
410 visit::walk_crate(&mut life_seeder, krate);
412 return life_seeder.worklist;
415 fn find_live(tcx: &ty::ctxt,
416 exported_items: &privacy::ExportedItems,
417 reachable_symbols: &NodeSet,
419 -> Box<HashSet<ast::NodeId>> {
420 let worklist = create_and_seed_worklist(tcx, exported_items,
421 reachable_symbols, krate);
422 let mut symbol_visitor = MarkSymbolVisitor::new(tcx, worklist);
423 symbol_visitor.mark_live_symbols();
424 symbol_visitor.live_symbols
427 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
429 hir::ItemStruct(ref struct_def, _) => struct_def.ctor_id,
434 struct DeadVisitor<'a, 'tcx: 'a> {
435 tcx: &'a ty::ctxt<'tcx>,
436 live_symbols: Box<HashSet<ast::NodeId>>,
439 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
440 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
441 let should_warn = match item.node {
446 | hir::ItemStruct(..) => true,
449 let ctor_id = get_struct_ctor_id(item);
450 should_warn && !self.symbol_is_live(item.id, ctor_id)
453 fn should_warn_about_field(&mut self, node: &hir::StructField_) -> bool {
454 let is_named = node.name().is_some();
455 let field_type = self.tcx.node_id_to_type(node.id);
456 let is_marker_field = match field_type.ty_to_def_id() {
457 Some(def_id) => self.tcx.lang_items.items().any(|(_, item)| *item == Some(def_id)),
461 && !self.symbol_is_live(node.id, None)
463 && !has_allow_dead_code_or_lang_attr(&node.attrs)
466 fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
467 !self.symbol_is_live(variant.id, None)
468 && !has_allow_dead_code_or_lang_attr(&variant.attrs)
471 // id := node id of an item's definition.
472 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
474 // If the item is a struct_ctor, then either its `id` or
475 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
476 // DefMap maps the ExprPath of a struct_ctor to the node referred by
477 // `ctor_id`. On the other hand, in a statement like
478 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
479 // DefMap maps <ty> to `id` instead.
480 fn symbol_is_live(&mut self,
482 ctor_id: Option<ast::NodeId>)
484 if self.live_symbols.contains(&id)
485 || ctor_id.map_or(false,
486 |ctor| self.live_symbols.contains(&ctor)) {
489 // If it's a type whose items are live, then it's live, too.
490 // This is done to handle the case where, for example, the static
491 // method of a private type is used, but the type itself is never
493 let impl_items = self.tcx.impl_items.borrow();
494 match self.tcx.inherent_impls.borrow().get(&self.tcx.map.local_def_id(id)) {
497 for impl_did in impl_list.iter() {
498 for item_did in impl_items.get(impl_did).unwrap().iter() {
499 if let Some(item_node_id) =
500 self.tcx.map.as_local_node_id(item_did.def_id()) {
501 if self.live_symbols.contains(&item_node_id) {
512 fn warn_dead_code(&mut self,
517 let name = name.as_str();
518 if !name.starts_with("_") {
521 .add_lint(lint::builtin::DEAD_CODE,
524 format!("{} is never used: `{}`", node_type, name));
529 impl<'a, 'tcx, 'v> Visitor<'v> for DeadVisitor<'a, 'tcx> {
530 fn visit_item(&mut self, item: &hir::Item) {
531 if self.should_warn_about_item(item) {
536 item.node.descriptive_variant()
540 hir::ItemEnum(ref enum_def, _) => {
541 for variant in &enum_def.variants {
542 if self.should_warn_about_variant(&variant.node) {
543 self.warn_dead_code(variant.node.id, variant.span,
544 variant.node.name, "variant");
551 visit::walk_item(self, item);
554 fn visit_foreign_item(&mut self, fi: &hir::ForeignItem) {
555 if !self.symbol_is_live(fi.id, None) {
556 self.warn_dead_code(fi.id, fi.span, fi.name, fi.node.descriptive_variant());
558 visit::walk_foreign_item(self, fi);
561 fn visit_struct_field(&mut self, field: &hir::StructField) {
562 if self.should_warn_about_field(&field.node) {
563 self.warn_dead_code(field.node.id, field.span,
564 field.node.name().unwrap(), "struct field");
567 visit::walk_struct_field(self, field);
570 fn visit_impl_item(&mut self, impl_item: &hir::ImplItem) {
571 match impl_item.node {
572 hir::ConstImplItem(_, ref expr) => {
573 if !self.symbol_is_live(impl_item.id, None) {
574 self.warn_dead_code(impl_item.id, impl_item.span,
575 impl_item.name, "associated const");
577 visit::walk_expr(self, expr)
579 hir::MethodImplItem(_, ref body) => {
580 if !self.symbol_is_live(impl_item.id, None) {
581 self.warn_dead_code(impl_item.id, impl_item.span,
582 impl_item.name, "method");
584 visit::walk_block(self, body)
586 hir::TypeImplItem(..) => {}
590 // Overwrite so that we don't warn the trait item itself.
591 fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
592 match trait_item.node {
593 hir::ConstTraitItem(_, Some(ref expr)) => {
594 visit::walk_expr(self, expr)
596 hir::MethodTraitItem(_, Some(ref body)) => {
597 visit::walk_block(self, body)
599 hir::ConstTraitItem(_, None) |
600 hir::MethodTraitItem(_, None) |
601 hir::TypeTraitItem(..) => {}
606 pub fn check_crate(tcx: &ty::ctxt,
607 exported_items: &privacy::ExportedItems,
608 reachable_symbols: &NodeSet) {
609 let krate = tcx.map.krate();
610 let live_symbols = find_live(tcx, exported_items,
611 reachable_symbols, krate);
612 let mut visitor = DeadVisitor { tcx: tcx, live_symbols: live_symbols };
613 visit::walk_crate(&mut visitor, krate);