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::intravisit::{self, Visitor};
19 use middle::{def, pat_util, privacy, ty};
20 use middle::def_id::{DefId};
23 use std::collections::HashSet;
24 use syntax::{ast, codemap};
25 use syntax::attr::{self, AttrMetaMethods};
27 // Any local node that may call something in its body block should be
28 // explored. For example, if it's a live NodeItem that is a
29 // function, then we should explore its block to check for codes that
30 // may need to be marked as live.
31 fn should_explore(tcx: &ty::ctxt, node_id: ast::NodeId) -> bool {
32 match tcx.map.find(node_id) {
33 Some(ast_map::NodeItem(..)) |
34 Some(ast_map::NodeImplItem(..)) |
35 Some(ast_map::NodeForeignItem(..)) |
36 Some(ast_map::NodeTraitItem(..)) =>
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 ignore_variant_stack: Vec<DefId>,
53 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
54 fn new(tcx: &'a ty::ctxt<'tcx>,
55 worklist: Vec<ast::NodeId>) -> MarkSymbolVisitor<'a, 'tcx> {
59 live_symbols: box HashSet::new(),
60 struct_has_extern_repr: false,
61 ignore_non_const_paths: false,
62 inherited_pub_visibility: false,
63 ignore_variant_stack: vec![],
67 fn check_def_id(&mut self, def_id: DefId) {
68 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
69 if should_explore(self.tcx, node_id) {
70 self.worklist.push(node_id);
72 self.live_symbols.insert(node_id);
76 fn insert_def_id(&mut self, def_id: DefId) {
77 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
78 debug_assert!(!should_explore(self.tcx, node_id));
79 self.live_symbols.insert(node_id);
83 fn lookup_and_handle_definition(&mut self, id: &ast::NodeId) {
84 use middle::ty::TypeVariants::{TyEnum, TyStruct};
86 // If `bar` is a trait item, make sure to mark Foo as alive in `Foo::bar`
87 self.tcx.tables.borrow().item_substs.get(id)
88 .and_then(|substs| substs.substs.self_ty())
89 .map(|ty| match ty.sty {
90 TyEnum(tyid, _) | TyStruct(tyid, _) => self.check_def_id(tyid.did),
94 self.tcx.def_map.borrow().get(id).map(|def| {
95 match def.full_def() {
96 def::DefConst(_) | def::DefAssociatedConst(..) => {
97 self.check_def_id(def.def_id());
99 _ if self.ignore_non_const_paths => (),
100 def::DefPrimTy(_) => (),
101 def::DefSelfTy(..) => (),
102 def::DefVariant(enum_id, variant_id, _) => {
103 self.check_def_id(enum_id);
104 if !self.ignore_variant_stack.contains(&variant_id) {
105 self.check_def_id(variant_id);
109 self.check_def_id(def.def_id());
115 fn lookup_and_handle_method(&mut self, id: ast::NodeId) {
116 let method_call = ty::MethodCall::expr(id);
117 let method = self.tcx.tables.borrow().method_map[&method_call];
118 self.check_def_id(method.def_id);
121 fn handle_field_access(&mut self, lhs: &hir::Expr, name: ast::Name) {
122 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
123 self.insert_def_id(def.struct_variant().field_named(name).did);
125 self.tcx.sess.span_bug(lhs.span, "named field access on non-struct")
129 fn handle_tup_field_access(&mut self, lhs: &hir::Expr, idx: usize) {
130 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
131 self.insert_def_id(def.struct_variant().fields[idx].did);
135 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat,
136 pats: &[codemap::Spanned<hir::FieldPat>]) {
137 let def = self.tcx.def_map.borrow().get(&lhs.id).unwrap().full_def();
138 let pat_ty = self.tcx.node_id_to_type(lhs.id);
139 let variant = match pat_ty.sty {
140 ty::TyStruct(adt, _) | ty::TyEnum(adt, _) => adt.variant_of_def(def),
141 _ => self.tcx.sess.span_bug(lhs.span, "non-ADT in struct pattern")
144 if let hir::PatWild = pat.node.pat.node {
147 self.insert_def_id(variant.field_named(pat.node.name).did);
151 fn mark_live_symbols(&mut self) {
152 let mut scanned = HashSet::new();
153 while !self.worklist.is_empty() {
154 let id = self.worklist.pop().unwrap();
155 if scanned.contains(&id) {
160 match self.tcx.map.find(id) {
162 self.live_symbols.insert(id);
163 self.visit_node(node);
170 fn visit_node(&mut self, node: &ast_map::Node) {
171 let had_extern_repr = self.struct_has_extern_repr;
172 self.struct_has_extern_repr = false;
173 let had_inherited_pub_visibility = self.inherited_pub_visibility;
174 self.inherited_pub_visibility = false;
176 ast_map::NodeItem(item) => {
178 hir::ItemStruct(..) => {
179 self.struct_has_extern_repr = item.attrs.iter().any(|attr| {
180 attr::find_repr_attrs(self.tcx.sess.diagnostic(), attr)
181 .contains(&attr::ReprExtern)
184 intravisit::walk_item(self, &*item);
186 hir::ItemEnum(..) => {
187 self.inherited_pub_visibility = item.vis == hir::Public;
188 intravisit::walk_item(self, &*item);
192 | hir::ItemStatic(..)
193 | hir::ItemConst(..) => {
194 intravisit::walk_item(self, &*item);
199 ast_map::NodeTraitItem(trait_item) => {
200 intravisit::walk_trait_item(self, trait_item);
202 ast_map::NodeImplItem(impl_item) => {
203 intravisit::walk_impl_item(self, impl_item);
205 ast_map::NodeForeignItem(foreign_item) => {
206 intravisit::walk_foreign_item(self, &*foreign_item);
210 self.struct_has_extern_repr = had_extern_repr;
211 self.inherited_pub_visibility = had_inherited_pub_visibility;
215 impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
217 fn visit_variant_data(&mut self, def: &hir::VariantData, _: ast::Name,
218 _: &hir::Generics, _: ast::NodeId, _: codemap::Span) {
219 let has_extern_repr = self.struct_has_extern_repr;
220 let inherited_pub_visibility = self.inherited_pub_visibility;
221 let live_fields = def.fields().iter().filter(|f| {
222 has_extern_repr || inherited_pub_visibility || match f.node.kind {
223 hir::NamedField(_, hir::Public) => true,
227 self.live_symbols.extend(live_fields.map(|f| f.node.id));
229 intravisit::walk_struct_def(self, def);
232 fn visit_expr(&mut self, expr: &hir::Expr) {
234 hir::ExprMethodCall(..) => {
235 self.lookup_and_handle_method(expr.id);
237 hir::ExprField(ref lhs, ref name) => {
238 self.handle_field_access(&**lhs, name.node);
240 hir::ExprTupField(ref lhs, idx) => {
241 self.handle_tup_field_access(&**lhs, idx.node);
246 intravisit::walk_expr(self, expr);
249 fn visit_arm(&mut self, arm: &hir::Arm) {
250 if arm.pats.len() == 1 {
251 let pat = &*arm.pats[0];
252 let variants = pat_util::necessary_variants(&self.tcx.def_map.borrow(), pat);
254 // Inside the body, ignore constructions of variants
255 // necessary for the pattern to match. Those construction sites
256 // can't be reached unless the variant is constructed elsewhere.
257 let len = self.ignore_variant_stack.len();
258 self.ignore_variant_stack.push_all(&*variants);
259 intravisit::walk_arm(self, arm);
260 self.ignore_variant_stack.truncate(len);
262 intravisit::walk_arm(self, arm);
266 fn visit_pat(&mut self, pat: &hir::Pat) {
267 let def_map = &self.tcx.def_map;
269 hir::PatStruct(_, ref fields, _) => {
270 self.handle_field_pattern_match(pat, fields);
272 _ if pat_util::pat_is_const(&def_map.borrow(), pat) => {
273 // it might be the only use of a const
274 self.lookup_and_handle_definition(&pat.id)
279 self.ignore_non_const_paths = true;
280 intravisit::walk_pat(self, pat);
281 self.ignore_non_const_paths = false;
284 fn visit_path(&mut self, path: &hir::Path, id: ast::NodeId) {
285 self.lookup_and_handle_definition(&id);
286 intravisit::walk_path(self, path);
289 fn visit_path_list_item(&mut self, path: &hir::Path, item: &hir::PathListItem) {
290 self.lookup_and_handle_definition(&item.node.id());
291 intravisit::walk_path_list_item(self, path, item);
295 fn has_allow_dead_code_or_lang_attr(attrs: &[ast::Attribute]) -> bool {
296 if attr::contains_name(attrs, "lang") {
300 let dead_code = lint::builtin::DEAD_CODE.name_lower();
301 for attr in lint::gather_attrs(attrs) {
303 Ok((ref name, lint::Allow, _))
304 if &name[..] == dead_code => return true,
311 // This visitor seeds items that
312 // 1) We want to explicitly consider as live:
313 // * Item annotated with #[allow(dead_code)]
314 // - This is done so that if we want to suppress warnings for a
315 // group of dead functions, we only have to annotate the "root".
316 // For example, if both `f` and `g` are dead and `f` calls `g`,
317 // then annotating `f` with `#[allow(dead_code)]` will suppress
318 // warning for both `f` and `g`.
319 // * Item annotated with #[lang=".."]
320 // - This is because lang items are always callable from elsewhere.
322 // 2) We are not sure to be live or not
323 // * Implementation of a trait method
325 worklist: Vec<ast::NodeId>
328 impl<'v> Visitor<'v> for LifeSeeder {
329 fn visit_item(&mut self, item: &hir::Item) {
330 let allow_dead_code = has_allow_dead_code_or_lang_attr(&item.attrs);
332 self.worklist.push(item.id);
335 hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
336 self.worklist.extend(enum_def.variants.iter()
337 .map(|variant| variant.node.data.id()));
339 hir::ItemTrait(_, _, _, ref trait_items) => {
340 for trait_item in trait_items {
341 match trait_item.node {
342 hir::ConstTraitItem(_, Some(_)) |
343 hir::MethodTraitItem(_, Some(_)) => {
344 if has_allow_dead_code_or_lang_attr(&trait_item.attrs) {
345 self.worklist.push(trait_item.id);
352 hir::ItemImpl(_, _, _, ref opt_trait, _, ref impl_items) => {
353 for impl_item in impl_items {
354 match impl_item.node {
355 hir::ImplItemKind::Const(..) |
356 hir::ImplItemKind::Method(..) => {
357 if opt_trait.is_some() ||
358 has_allow_dead_code_or_lang_attr(&impl_item.attrs) {
359 self.worklist.push(impl_item.id);
362 hir::ImplItemKind::Type(_) => {}
371 fn create_and_seed_worklist(tcx: &ty::ctxt,
372 access_levels: &privacy::AccessLevels,
373 krate: &hir::Crate) -> Vec<ast::NodeId> {
374 let mut worklist = Vec::new();
375 for (id, _) in &access_levels.map {
380 match *tcx.sess.entry_fn.borrow() {
381 Some((id, _)) => worklist.push(id),
385 // Seed implemented trait items
386 let mut life_seeder = LifeSeeder {
389 krate.visit_all_items(&mut life_seeder);
391 return life_seeder.worklist;
394 fn find_live(tcx: &ty::ctxt,
395 access_levels: &privacy::AccessLevels,
397 -> Box<HashSet<ast::NodeId>> {
398 let worklist = create_and_seed_worklist(tcx, access_levels, krate);
399 let mut symbol_visitor = MarkSymbolVisitor::new(tcx, worklist);
400 symbol_visitor.mark_live_symbols();
401 symbol_visitor.live_symbols
404 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
406 hir::ItemStruct(ref struct_def, _) if !struct_def.is_struct() => {
407 Some(struct_def.id())
413 struct DeadVisitor<'a, 'tcx: 'a> {
414 tcx: &'a ty::ctxt<'tcx>,
415 live_symbols: Box<HashSet<ast::NodeId>>,
418 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
419 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
420 let should_warn = match item.node {
425 | hir::ItemStruct(..) => true,
428 let ctor_id = get_struct_ctor_id(item);
429 should_warn && !self.symbol_is_live(item.id, ctor_id)
432 fn should_warn_about_field(&mut self, node: &hir::StructField_) -> bool {
433 let is_named = node.name().is_some();
434 let field_type = self.tcx.node_id_to_type(node.id);
435 let is_marker_field = match field_type.ty_to_def_id() {
436 Some(def_id) => self.tcx.lang_items.items().any(|(_, item)| *item == Some(def_id)),
440 && !self.symbol_is_live(node.id, None)
442 && !has_allow_dead_code_or_lang_attr(&node.attrs)
445 fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
446 !self.symbol_is_live(variant.data.id(), None)
447 && !has_allow_dead_code_or_lang_attr(&variant.attrs)
450 // id := node id of an item's definition.
451 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
453 // If the item is a struct_ctor, then either its `id` or
454 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
455 // DefMap maps the ExprPath of a struct_ctor to the node referred by
456 // `ctor_id`. On the other hand, in a statement like
457 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
458 // DefMap maps <ty> to `id` instead.
459 fn symbol_is_live(&mut self,
461 ctor_id: Option<ast::NodeId>)
463 if self.live_symbols.contains(&id)
464 || ctor_id.map_or(false,
465 |ctor| self.live_symbols.contains(&ctor)) {
468 // If it's a type whose items are live, then it's live, too.
469 // This is done to handle the case where, for example, the static
470 // method of a private type is used, but the type itself is never
472 let impl_items = self.tcx.impl_items.borrow();
473 match self.tcx.inherent_impls.borrow().get(&self.tcx.map.local_def_id(id)) {
476 for impl_did in impl_list.iter() {
477 for item_did in impl_items.get(impl_did).unwrap().iter() {
478 if let Some(item_node_id) =
479 self.tcx.map.as_local_node_id(item_did.def_id()) {
480 if self.live_symbols.contains(&item_node_id) {
491 fn warn_dead_code(&mut self,
496 let name = name.as_str();
497 if !name.starts_with("_") {
500 .add_lint(lint::builtin::DEAD_CODE,
503 format!("{} is never used: `{}`", node_type, name));
508 impl<'a, 'tcx, 'v> Visitor<'v> for DeadVisitor<'a, 'tcx> {
509 /// Walk nested items in place so that we don't report dead-code
510 /// on inner functions when the outer function is already getting
511 /// an error. We could do this also by checking the parents, but
512 /// this is how the code is setup and it seems harmless enough.
513 fn visit_nested_item(&mut self, item: hir::ItemId) {
514 self.visit_item(self.tcx.map.expect_item(item.id))
517 fn visit_item(&mut self, item: &hir::Item) {
518 if self.should_warn_about_item(item) {
523 item.node.descriptive_variant()
526 // Only continue if we didn't warn
527 intravisit::walk_item(self, item);
531 fn visit_variant(&mut self, variant: &hir::Variant, g: &hir::Generics, id: ast::NodeId) {
532 if self.should_warn_about_variant(&variant.node) {
533 self.warn_dead_code(variant.node.data.id(), variant.span,
534 variant.node.name, "variant");
536 intravisit::walk_variant(self, variant, g, id);
540 fn visit_foreign_item(&mut self, fi: &hir::ForeignItem) {
541 if !self.symbol_is_live(fi.id, None) {
542 self.warn_dead_code(fi.id, fi.span, fi.name, fi.node.descriptive_variant());
544 intravisit::walk_foreign_item(self, fi);
547 fn visit_struct_field(&mut self, field: &hir::StructField) {
548 if self.should_warn_about_field(&field.node) {
549 self.warn_dead_code(field.node.id, field.span,
550 field.node.name().unwrap(), "struct field");
553 intravisit::walk_struct_field(self, field);
556 fn visit_impl_item(&mut self, impl_item: &hir::ImplItem) {
557 match impl_item.node {
558 hir::ImplItemKind::Const(_, ref expr) => {
559 if !self.symbol_is_live(impl_item.id, None) {
560 self.warn_dead_code(impl_item.id, impl_item.span,
561 impl_item.name, "associated const");
563 intravisit::walk_expr(self, expr)
565 hir::ImplItemKind::Method(_, ref body) => {
566 if !self.symbol_is_live(impl_item.id, None) {
567 self.warn_dead_code(impl_item.id, impl_item.span,
568 impl_item.name, "method");
570 intravisit::walk_block(self, body)
572 hir::ImplItemKind::Type(..) => {}
576 // Overwrite so that we don't warn the trait item itself.
577 fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
578 match trait_item.node {
579 hir::ConstTraitItem(_, Some(ref expr)) => {
580 intravisit::walk_expr(self, expr)
582 hir::MethodTraitItem(_, Some(ref body)) => {
583 intravisit::walk_block(self, body)
585 hir::ConstTraitItem(_, None) |
586 hir::MethodTraitItem(_, None) |
587 hir::TypeTraitItem(..) => {}
592 pub fn check_crate(tcx: &ty::ctxt, access_levels: &privacy::AccessLevels) {
593 let krate = tcx.map.krate();
594 let live_symbols = find_live(tcx, access_levels, krate);
595 let mut visitor = DeadVisitor { tcx: tcx, live_symbols: live_symbols };
596 intravisit::walk_crate(&mut visitor, krate);