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 dep_graph::DepNode;
16 use front::map as ast_map;
18 use rustc_front::intravisit::{self, Visitor};
20 use middle::{pat_util, privacy, ty};
22 use middle::def_id::{DefId};
25 use std::collections::HashSet;
26 use syntax::{ast, codemap};
27 use syntax::attr::{self, AttrMetaMethods};
29 // Any local node that may call something in its body block should be
30 // explored. For example, if it's a live NodeItem that is a
31 // function, then we should explore its block to check for codes that
32 // may need to be marked as live.
33 fn should_explore(tcx: &ty::ctxt, node_id: ast::NodeId) -> bool {
34 match tcx.map.find(node_id) {
35 Some(ast_map::NodeItem(..)) |
36 Some(ast_map::NodeImplItem(..)) |
37 Some(ast_map::NodeForeignItem(..)) |
38 Some(ast_map::NodeTraitItem(..)) =>
45 struct MarkSymbolVisitor<'a, 'tcx: 'a> {
46 worklist: Vec<ast::NodeId>,
47 tcx: &'a ty::ctxt<'tcx>,
48 live_symbols: Box<HashSet<ast::NodeId>>,
49 struct_has_extern_repr: bool,
50 ignore_non_const_paths: bool,
51 inherited_pub_visibility: bool,
52 ignore_variant_stack: Vec<DefId>,
55 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
56 fn new(tcx: &'a ty::ctxt<'tcx>,
57 worklist: Vec<ast::NodeId>) -> MarkSymbolVisitor<'a, 'tcx> {
61 live_symbols: box HashSet::new(),
62 struct_has_extern_repr: false,
63 ignore_non_const_paths: false,
64 inherited_pub_visibility: false,
65 ignore_variant_stack: vec![],
69 fn check_def_id(&mut self, def_id: DefId) {
70 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
71 if should_explore(self.tcx, node_id) {
72 self.worklist.push(node_id);
74 self.live_symbols.insert(node_id);
78 fn insert_def_id(&mut self, def_id: DefId) {
79 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
80 debug_assert!(!should_explore(self.tcx, node_id));
81 self.live_symbols.insert(node_id);
85 fn lookup_and_handle_definition(&mut self, id: &ast::NodeId) {
86 use middle::ty::TypeVariants::{TyEnum, TyStruct};
88 // If `bar` is a trait item, make sure to mark Foo as alive in `Foo::bar`
89 self.tcx.tables.borrow().item_substs.get(id)
90 .and_then(|substs| substs.substs.self_ty())
91 .map(|ty| match ty.sty {
92 TyEnum(tyid, _) | TyStruct(tyid, _) => self.check_def_id(tyid.did),
96 self.tcx.def_map.borrow().get(id).map(|def| {
97 match def.full_def() {
98 Def::Const(_) | Def::AssociatedConst(..) => {
99 self.check_def_id(def.def_id());
101 _ if self.ignore_non_const_paths => (),
102 Def::PrimTy(_) => (),
103 Def::SelfTy(..) => (),
104 Def::Variant(enum_id, variant_id) => {
105 self.check_def_id(enum_id);
106 if !self.ignore_variant_stack.contains(&variant_id) {
107 self.check_def_id(variant_id);
111 self.check_def_id(def.def_id());
117 fn lookup_and_handle_method(&mut self, id: ast::NodeId) {
118 let method_call = ty::MethodCall::expr(id);
119 let method = self.tcx.tables.borrow().method_map[&method_call];
120 self.check_def_id(method.def_id);
123 fn handle_field_access(&mut self, lhs: &hir::Expr, name: ast::Name) {
124 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
125 self.insert_def_id(def.struct_variant().field_named(name).did);
127 self.tcx.sess.span_bug(lhs.span, "named field access on non-struct")
131 fn handle_tup_field_access(&mut self, lhs: &hir::Expr, idx: usize) {
132 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
133 self.insert_def_id(def.struct_variant().fields[idx].did);
137 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat,
138 pats: &[codemap::Spanned<hir::FieldPat>]) {
139 let def = self.tcx.def_map.borrow().get(&lhs.id).unwrap().full_def();
140 let pat_ty = self.tcx.node_id_to_type(lhs.id);
141 let variant = match pat_ty.sty {
142 ty::TyStruct(adt, _) | ty::TyEnum(adt, _) => adt.variant_of_def(def),
143 _ => self.tcx.sess.span_bug(lhs.span, "non-ADT in struct pattern")
146 if let hir::PatWild = pat.node.pat.node {
149 self.insert_def_id(variant.field_named(pat.node.name).did);
153 fn mark_live_symbols(&mut self) {
154 let mut scanned = HashSet::new();
155 while !self.worklist.is_empty() {
156 let id = self.worklist.pop().unwrap();
157 if scanned.contains(&id) {
162 match self.tcx.map.find(id) {
164 self.live_symbols.insert(id);
165 self.visit_node(node);
172 fn visit_node(&mut self, node: &ast_map::Node) {
173 let had_extern_repr = self.struct_has_extern_repr;
174 self.struct_has_extern_repr = false;
175 let had_inherited_pub_visibility = self.inherited_pub_visibility;
176 self.inherited_pub_visibility = false;
178 ast_map::NodeItem(item) => {
180 hir::ItemStruct(..) => {
181 self.struct_has_extern_repr = item.attrs.iter().any(|attr| {
182 attr::find_repr_attrs(self.tcx.sess.diagnostic(), attr)
183 .contains(&attr::ReprExtern)
186 intravisit::walk_item(self, &*item);
188 hir::ItemEnum(..) => {
189 self.inherited_pub_visibility = item.vis == hir::Public;
190 intravisit::walk_item(self, &*item);
194 | hir::ItemStatic(..)
195 | hir::ItemConst(..) => {
196 intravisit::walk_item(self, &*item);
201 ast_map::NodeTraitItem(trait_item) => {
202 intravisit::walk_trait_item(self, trait_item);
204 ast_map::NodeImplItem(impl_item) => {
205 intravisit::walk_impl_item(self, impl_item);
207 ast_map::NodeForeignItem(foreign_item) => {
208 intravisit::walk_foreign_item(self, &*foreign_item);
212 self.struct_has_extern_repr = had_extern_repr;
213 self.inherited_pub_visibility = had_inherited_pub_visibility;
217 impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
219 fn visit_variant_data(&mut self, def: &hir::VariantData, _: ast::Name,
220 _: &hir::Generics, _: ast::NodeId, _: codemap::Span) {
221 let has_extern_repr = self.struct_has_extern_repr;
222 let inherited_pub_visibility = self.inherited_pub_visibility;
223 let live_fields = def.fields().iter().filter(|f| {
224 has_extern_repr || inherited_pub_visibility || match f.node.kind {
225 hir::NamedField(_, hir::Public) => true,
229 self.live_symbols.extend(live_fields.map(|f| f.node.id));
231 intravisit::walk_struct_def(self, def);
234 fn visit_expr(&mut self, expr: &hir::Expr) {
236 hir::ExprMethodCall(..) => {
237 self.lookup_and_handle_method(expr.id);
239 hir::ExprField(ref lhs, ref name) => {
240 self.handle_field_access(&**lhs, name.node);
242 hir::ExprTupField(ref lhs, idx) => {
243 self.handle_tup_field_access(&**lhs, idx.node);
248 intravisit::walk_expr(self, expr);
251 fn visit_arm(&mut self, arm: &hir::Arm) {
252 if arm.pats.len() == 1 {
253 let pat = &*arm.pats[0];
254 let variants = pat_util::necessary_variants(&self.tcx.def_map.borrow(), pat);
256 // Inside the body, ignore constructions of variants
257 // necessary for the pattern to match. Those construction sites
258 // can't be reached unless the variant is constructed elsewhere.
259 let len = self.ignore_variant_stack.len();
260 self.ignore_variant_stack.extend_from_slice(&*variants);
261 intravisit::walk_arm(self, arm);
262 self.ignore_variant_stack.truncate(len);
264 intravisit::walk_arm(self, arm);
268 fn visit_pat(&mut self, pat: &hir::Pat) {
269 let def_map = &self.tcx.def_map;
271 hir::PatStruct(_, ref fields, _) => {
272 self.handle_field_pattern_match(pat, fields);
274 _ if pat_util::pat_is_const(&def_map.borrow(), pat) => {
275 // it might be the only use of a const
276 self.lookup_and_handle_definition(&pat.id)
281 self.ignore_non_const_paths = true;
282 intravisit::walk_pat(self, pat);
283 self.ignore_non_const_paths = false;
286 fn visit_path(&mut self, path: &hir::Path, id: ast::NodeId) {
287 self.lookup_and_handle_definition(&id);
288 intravisit::walk_path(self, path);
291 fn visit_path_list_item(&mut self, path: &hir::Path, item: &hir::PathListItem) {
292 self.lookup_and_handle_definition(&item.node.id());
293 intravisit::walk_path_list_item(self, path, item);
297 fn has_allow_dead_code_or_lang_attr(attrs: &[ast::Attribute]) -> bool {
298 if attr::contains_name(attrs, "lang") {
302 let dead_code = lint::builtin::DEAD_CODE.name_lower();
303 for attr in lint::gather_attrs(attrs) {
305 Ok((ref name, lint::Allow, _))
306 if &name[..] == dead_code => return true,
313 // This visitor seeds items that
314 // 1) We want to explicitly consider as live:
315 // * Item annotated with #[allow(dead_code)]
316 // - This is done so that if we want to suppress warnings for a
317 // group of dead functions, we only have to annotate the "root".
318 // For example, if both `f` and `g` are dead and `f` calls `g`,
319 // then annotating `f` with `#[allow(dead_code)]` will suppress
320 // warning for both `f` and `g`.
321 // * Item annotated with #[lang=".."]
322 // - This is because lang items are always callable from elsewhere.
324 // 2) We are not sure to be live or not
325 // * Implementation of a trait method
327 worklist: Vec<ast::NodeId>
330 impl<'v> Visitor<'v> for LifeSeeder {
331 fn visit_item(&mut self, item: &hir::Item) {
332 let allow_dead_code = has_allow_dead_code_or_lang_attr(&item.attrs);
334 self.worklist.push(item.id);
337 hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
338 self.worklist.extend(enum_def.variants.iter()
339 .map(|variant| variant.node.data.id()));
341 hir::ItemTrait(_, _, _, ref trait_items) => {
342 for trait_item in trait_items {
343 match trait_item.node {
344 hir::ConstTraitItem(_, Some(_)) |
345 hir::MethodTraitItem(_, Some(_)) => {
346 if has_allow_dead_code_or_lang_attr(&trait_item.attrs) {
347 self.worklist.push(trait_item.id);
354 hir::ItemImpl(_, _, _, ref opt_trait, _, ref impl_items) => {
355 for impl_item in impl_items {
356 match impl_item.node {
357 hir::ImplItemKind::Const(..) |
358 hir::ImplItemKind::Method(..) => {
359 if opt_trait.is_some() ||
360 has_allow_dead_code_or_lang_attr(&impl_item.attrs) {
361 self.worklist.push(impl_item.id);
364 hir::ImplItemKind::Type(_) => {}
373 fn create_and_seed_worklist(tcx: &ty::ctxt,
374 access_levels: &privacy::AccessLevels,
375 krate: &hir::Crate) -> Vec<ast::NodeId> {
376 let mut worklist = Vec::new();
377 for (id, _) in &access_levels.map {
382 match *tcx.sess.entry_fn.borrow() {
383 Some((id, _)) => worklist.push(id),
387 // Seed implemented trait items
388 let mut life_seeder = LifeSeeder {
391 krate.visit_all_items(&mut life_seeder);
393 return life_seeder.worklist;
396 fn find_live(tcx: &ty::ctxt,
397 access_levels: &privacy::AccessLevels,
399 -> Box<HashSet<ast::NodeId>> {
400 let worklist = create_and_seed_worklist(tcx, access_levels, krate);
401 let mut symbol_visitor = MarkSymbolVisitor::new(tcx, worklist);
402 symbol_visitor.mark_live_symbols();
403 symbol_visitor.live_symbols
406 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
408 hir::ItemStruct(ref struct_def, _) if !struct_def.is_struct() => {
409 Some(struct_def.id())
415 struct DeadVisitor<'a, 'tcx: 'a> {
416 tcx: &'a ty::ctxt<'tcx>,
417 live_symbols: Box<HashSet<ast::NodeId>>,
420 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
421 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
422 let should_warn = match item.node {
427 | hir::ItemStruct(..) => true,
430 let ctor_id = get_struct_ctor_id(item);
431 should_warn && !self.symbol_is_live(item.id, ctor_id)
434 fn should_warn_about_field(&mut self, node: &hir::StructField_) -> bool {
435 let is_named = node.name().is_some();
436 let field_type = self.tcx.node_id_to_type(node.id);
437 let is_marker_field = match field_type.ty_to_def_id() {
438 Some(def_id) => self.tcx.lang_items.items().any(|(_, item)| *item == Some(def_id)),
442 && !self.symbol_is_live(node.id, None)
444 && !has_allow_dead_code_or_lang_attr(&node.attrs)
447 fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
448 !self.symbol_is_live(variant.data.id(), None)
449 && !has_allow_dead_code_or_lang_attr(&variant.attrs)
452 // id := node id of an item's definition.
453 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
455 // If the item is a struct_ctor, then either its `id` or
456 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
457 // DefMap maps the ExprPath of a struct_ctor to the node referred by
458 // `ctor_id`. On the other hand, in a statement like
459 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
460 // DefMap maps <ty> to `id` instead.
461 fn symbol_is_live(&mut self,
463 ctor_id: Option<ast::NodeId>)
465 if self.live_symbols.contains(&id)
466 || ctor_id.map_or(false,
467 |ctor| self.live_symbols.contains(&ctor)) {
470 // If it's a type whose items are live, then it's live, too.
471 // This is done to handle the case where, for example, the static
472 // method of a private type is used, but the type itself is never
474 let impl_items = self.tcx.impl_items.borrow();
475 match self.tcx.inherent_impls.borrow().get(&self.tcx.map.local_def_id(id)) {
478 for impl_did in impl_list.iter() {
479 for item_did in impl_items.get(impl_did).unwrap().iter() {
480 if let Some(item_node_id) =
481 self.tcx.map.as_local_node_id(item_did.def_id()) {
482 if self.live_symbols.contains(&item_node_id) {
493 fn warn_dead_code(&mut self,
498 let name = name.as_str();
499 if !name.starts_with("_") {
502 .add_lint(lint::builtin::DEAD_CODE,
505 format!("{} is never used: `{}`", node_type, name));
510 impl<'a, 'tcx, 'v> Visitor<'v> for DeadVisitor<'a, 'tcx> {
511 /// Walk nested items in place so that we don't report dead-code
512 /// on inner functions when the outer function is already getting
513 /// an error. We could do this also by checking the parents, but
514 /// this is how the code is setup and it seems harmless enough.
515 fn visit_nested_item(&mut self, item: hir::ItemId) {
516 self.visit_item(self.tcx.map.expect_item(item.id))
519 fn visit_item(&mut self, item: &hir::Item) {
520 if self.should_warn_about_item(item) {
525 item.node.descriptive_variant()
528 // Only continue if we didn't warn
529 intravisit::walk_item(self, item);
533 fn visit_variant(&mut self, variant: &hir::Variant, g: &hir::Generics, id: ast::NodeId) {
534 if self.should_warn_about_variant(&variant.node) {
535 self.warn_dead_code(variant.node.data.id(), variant.span,
536 variant.node.name, "variant");
538 intravisit::walk_variant(self, variant, g, id);
542 fn visit_foreign_item(&mut self, fi: &hir::ForeignItem) {
543 if !self.symbol_is_live(fi.id, None) {
544 self.warn_dead_code(fi.id, fi.span, fi.name, fi.node.descriptive_variant());
546 intravisit::walk_foreign_item(self, fi);
549 fn visit_struct_field(&mut self, field: &hir::StructField) {
550 if self.should_warn_about_field(&field.node) {
551 self.warn_dead_code(field.node.id, field.span,
552 field.node.name().unwrap(), "struct field");
555 intravisit::walk_struct_field(self, field);
558 fn visit_impl_item(&mut self, impl_item: &hir::ImplItem) {
559 match impl_item.node {
560 hir::ImplItemKind::Const(_, ref expr) => {
561 if !self.symbol_is_live(impl_item.id, None) {
562 self.warn_dead_code(impl_item.id, impl_item.span,
563 impl_item.name, "associated const");
565 intravisit::walk_expr(self, expr)
567 hir::ImplItemKind::Method(_, ref body) => {
568 if !self.symbol_is_live(impl_item.id, None) {
569 self.warn_dead_code(impl_item.id, impl_item.span,
570 impl_item.name, "method");
572 intravisit::walk_block(self, body)
574 hir::ImplItemKind::Type(..) => {}
578 // Overwrite so that we don't warn the trait item itself.
579 fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
580 match trait_item.node {
581 hir::ConstTraitItem(_, Some(ref expr)) => {
582 intravisit::walk_expr(self, expr)
584 hir::MethodTraitItem(_, Some(ref body)) => {
585 intravisit::walk_block(self, body)
587 hir::ConstTraitItem(_, None) |
588 hir::MethodTraitItem(_, None) |
589 hir::TypeTraitItem(..) => {}
594 pub fn check_crate(tcx: &ty::ctxt, access_levels: &privacy::AccessLevels) {
595 let _task = tcx.dep_graph.in_task(DepNode::DeadCheck);
596 let krate = tcx.map.krate();
597 let live_symbols = find_live(tcx, access_levels, krate);
598 let mut visitor = DeadVisitor { tcx: tcx, live_symbols: live_symbols };
599 intravisit::walk_crate(&mut visitor, krate);