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 hir::map as hir_map;
16 use hir::{self, Item_, PatKind};
17 use hir::intravisit::{self, Visitor, NestedVisitorMap};
18 use hir::itemlikevisit::ItemLikeVisitor;
21 use hir::def_id::{DefId, LOCAL_CRATE};
24 use ty::{self, TyCtxt};
25 use util::nodemap::FxHashSet;
27 use syntax::{ast, codemap};
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(..)) =>
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 ignore_non_const_paths: bool,
55 inherited_pub_visibility: bool,
56 ignore_variant_stack: Vec<DefId>,
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);
65 self.live_symbols.insert(node_id);
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);
76 fn handle_definition(&mut self, def: Def) {
78 Def::Const(_) | Def::AssociatedConst(..) => {
79 self.check_def_id(def.def_id());
81 _ if self.ignore_non_const_paths => (),
82 Def::PrimTy(..) | Def::SelfTy(..) => (),
83 Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
84 if let Some(enum_id) = self.tcx.parent_def_id(variant_id) {
85 self.check_def_id(enum_id);
87 if !self.ignore_variant_stack.contains(&variant_id) {
88 self.check_def_id(variant_id);
92 self.check_def_id(def.def_id());
97 fn lookup_and_handle_method(&mut self, id: hir::HirId) {
98 self.check_def_id(self.tables.type_dependent_defs()[id].def_id());
101 fn handle_field_access(&mut self, lhs: &hir::Expr, name: ast::Name) {
102 match self.tables.expr_ty_adjusted(lhs).sty {
103 ty::TyAdt(def, _) => {
104 self.insert_def_id(def.struct_variant().field_named(name).did);
106 _ => span_bug!(lhs.span, "named field access on non-ADT"),
110 fn handle_tup_field_access(&mut self, lhs: &hir::Expr, idx: usize) {
111 match self.tables.expr_ty_adjusted(lhs).sty {
112 ty::TyAdt(def, _) => {
113 self.insert_def_id(def.struct_variant().fields[idx].did);
115 ty::TyTuple(..) => {}
116 _ => span_bug!(lhs.span, "numeric field access on non-ADT"),
120 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat, def: Def,
121 pats: &[codemap::Spanned<hir::FieldPat>]) {
122 let variant = match self.tables.node_id_to_type(lhs.hir_id).sty {
123 ty::TyAdt(adt, _) => adt.variant_of_def(def),
124 _ => span_bug!(lhs.span, "non-ADT in struct pattern")
127 if let PatKind::Wild = pat.node.pat.node {
130 self.insert_def_id(variant.field_named(pat.node.name).did);
134 fn mark_live_symbols(&mut self) {
135 let mut scanned = FxHashSet();
136 while !self.worklist.is_empty() {
137 let id = self.worklist.pop().unwrap();
138 if scanned.contains(&id) {
143 if let Some(ref node) = self.tcx.hir.find(id) {
144 self.live_symbols.insert(id);
145 self.visit_node(node);
150 fn visit_node(&mut self, node: &hir_map::Node<'tcx>) {
151 let had_extern_repr = self.struct_has_extern_repr;
152 self.struct_has_extern_repr = false;
153 let had_inherited_pub_visibility = self.inherited_pub_visibility;
154 self.inherited_pub_visibility = false;
156 hir_map::NodeItem(item) => {
158 hir::ItemStruct(..) | hir::ItemUnion(..) => {
159 let def_id = self.tcx.hir.local_def_id(item.id);
160 let def = self.tcx.adt_def(def_id);
161 self.struct_has_extern_repr = def.repr.c();
163 intravisit::walk_item(self, &item);
165 hir::ItemEnum(..) => {
166 self.inherited_pub_visibility = item.vis == hir::Public;
167 intravisit::walk_item(self, &item);
171 | hir::ItemStatic(..)
172 | hir::ItemConst(..) => {
173 intravisit::walk_item(self, &item);
178 hir_map::NodeTraitItem(trait_item) => {
179 intravisit::walk_trait_item(self, trait_item);
181 hir_map::NodeImplItem(impl_item) => {
182 intravisit::walk_impl_item(self, impl_item);
184 hir_map::NodeForeignItem(foreign_item) => {
185 intravisit::walk_foreign_item(self, &foreign_item);
189 self.struct_has_extern_repr = had_extern_repr;
190 self.inherited_pub_visibility = had_inherited_pub_visibility;
193 fn mark_as_used_if_union(&mut self, did: DefId, fields: &hir::HirVec<hir::Field>) {
194 if let Some(node_id) = self.tcx.hir.as_local_node_id(did) {
195 if let Some(hir_map::NodeItem(item)) = self.tcx.hir.find(node_id) {
196 if let Item_::ItemUnion(ref variant, _) = item.node {
197 if variant.fields().len() > 1 {
198 for field in variant.fields() {
199 if fields.iter().find(|x| x.name.node == field.name).is_some() {
200 self.live_symbols.insert(field.id);
210 impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
211 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
212 NestedVisitorMap::None
215 fn visit_nested_body(&mut self, body: hir::BodyId) {
216 let old_tables = self.tables;
217 self.tables = self.tcx.body_tables(body);
218 let body = self.tcx.hir.body(body);
219 self.visit_body(body);
220 self.tables = old_tables;
223 fn visit_variant_data(&mut self, def: &'tcx hir::VariantData, _: ast::Name,
224 _: &hir::Generics, _: ast::NodeId, _: syntax_pos::Span) {
225 let has_extern_repr = self.struct_has_extern_repr;
226 let inherited_pub_visibility = self.inherited_pub_visibility;
227 let live_fields = def.fields().iter().filter(|f| {
228 has_extern_repr || inherited_pub_visibility || f.vis == hir::Public
230 self.live_symbols.extend(live_fields.map(|f| f.id));
232 intravisit::walk_struct_def(self, def);
235 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
237 hir::ExprPath(ref qpath @ hir::QPath::TypeRelative(..)) => {
238 let def = self.tables.qpath_def(qpath, expr.hir_id);
239 self.handle_definition(def);
241 hir::ExprMethodCall(..) => {
242 self.lookup_and_handle_method(expr.hir_id);
244 hir::ExprField(ref lhs, ref name) => {
245 self.handle_field_access(&lhs, name.node);
247 hir::ExprTupField(ref lhs, idx) => {
248 self.handle_tup_field_access(&lhs, idx.node);
250 hir::ExprStruct(_, ref fields, _) => {
251 if let ty::TypeVariants::TyAdt(ref def, _) = self.tables.expr_ty(expr).sty {
253 self.mark_as_used_if_union(def.did, fields);
260 intravisit::walk_expr(self, expr);
263 fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
264 if arm.pats.len() == 1 {
265 let variants = arm.pats[0].necessary_variants();
267 // Inside the body, ignore constructions of variants
268 // necessary for the pattern to match. Those construction sites
269 // can't be reached unless the variant is constructed elsewhere.
270 let len = self.ignore_variant_stack.len();
271 self.ignore_variant_stack.extend_from_slice(&variants);
272 intravisit::walk_arm(self, arm);
273 self.ignore_variant_stack.truncate(len);
275 intravisit::walk_arm(self, arm);
279 fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
281 PatKind::Struct(hir::QPath::Resolved(_, ref path), ref fields, _) => {
282 self.handle_field_pattern_match(pat, path.def, fields);
284 PatKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
285 let def = self.tables.qpath_def(qpath, pat.hir_id);
286 self.handle_definition(def);
291 self.ignore_non_const_paths = true;
292 intravisit::walk_pat(self, pat);
293 self.ignore_non_const_paths = false;
296 fn visit_path(&mut self, path: &'tcx hir::Path, _: ast::NodeId) {
297 self.handle_definition(path.def);
298 intravisit::walk_path(self, path);
302 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt,
304 attrs: &[ast::Attribute]) -> bool {
305 if attr::contains_name(attrs, "lang") {
309 // #[used] also keeps the item alive forcefully,
310 // e.g. for placing it in a specific section.
311 if attr::contains_name(attrs, "used") {
315 // Don't lint about global allocators
316 if attr::contains_name(attrs, "global_allocator") {
320 tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
323 // This visitor seeds items that
324 // 1) We want to explicitly consider as live:
325 // * Item annotated with #[allow(dead_code)]
326 // - This is done so that if we want to suppress warnings for a
327 // group of dead functions, we only have to annotate the "root".
328 // For example, if both `f` and `g` are dead and `f` calls `g`,
329 // then annotating `f` with `#[allow(dead_code)]` will suppress
330 // warning for both `f` and `g`.
331 // * Item annotated with #[lang=".."]
332 // - This is because lang items are always callable from elsewhere.
334 // 2) We are not sure to be live or not
335 // * Implementation of a trait method
336 struct LifeSeeder<'k, 'tcx: 'k> {
337 worklist: Vec<ast::NodeId>,
338 krate: &'k hir::Crate,
339 tcx: TyCtxt<'k, 'tcx, 'tcx>,
342 impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
343 fn visit_item(&mut self, item: &hir::Item) {
344 let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx,
348 self.worklist.push(item.id);
351 hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
352 self.worklist.extend(enum_def.variants.iter()
353 .map(|variant| variant.node.data.id()));
355 hir::ItemTrait(.., ref trait_item_refs) => {
356 for trait_item_ref in trait_item_refs {
357 let trait_item = self.krate.trait_item(trait_item_ref.id);
358 match trait_item.node {
359 hir::TraitItemKind::Const(_, Some(_)) |
360 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
361 if has_allow_dead_code_or_lang_attr(self.tcx,
364 self.worklist.push(trait_item.id);
371 hir::ItemImpl(.., ref opt_trait, _, ref impl_item_refs) => {
372 for impl_item_ref in impl_item_refs {
373 let impl_item = self.krate.impl_item(impl_item_ref.id);
374 if opt_trait.is_some() ||
375 has_allow_dead_code_or_lang_attr(self.tcx,
378 self.worklist.push(impl_item_ref.id.node_id);
386 fn visit_trait_item(&mut self, _item: &hir::TraitItem) {
387 // ignore: we are handling this in `visit_item` above
390 fn visit_impl_item(&mut self, _item: &hir::ImplItem) {
391 // ignore: we are handling this in `visit_item` above
395 fn create_and_seed_worklist<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
396 access_levels: &privacy::AccessLevels,
398 -> Vec<ast::NodeId> {
399 let mut worklist = Vec::new();
400 for (id, _) in &access_levels.map {
405 if let Some((id, _)) = *tcx.sess.entry_fn.borrow() {
409 // Seed implemented trait items
410 let mut life_seeder = LifeSeeder {
415 krate.visit_all_item_likes(&mut life_seeder);
417 return life_seeder.worklist;
420 fn find_live<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
421 access_levels: &privacy::AccessLevels,
423 -> Box<FxHashSet<ast::NodeId>> {
424 let worklist = create_and_seed_worklist(tcx, access_levels, krate);
425 let mut symbol_visitor = MarkSymbolVisitor {
428 tables: &ty::TypeckTables::empty(None),
429 live_symbols: box FxHashSet(),
430 struct_has_extern_repr: false,
431 ignore_non_const_paths: false,
432 inherited_pub_visibility: false,
433 ignore_variant_stack: vec![],
435 symbol_visitor.mark_live_symbols();
436 symbol_visitor.live_symbols
439 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
441 hir::ItemStruct(ref struct_def, _) if !struct_def.is_struct() => {
442 Some(struct_def.id())
448 struct DeadVisitor<'a, 'tcx: 'a> {
449 tcx: TyCtxt<'a, 'tcx, 'tcx>,
450 live_symbols: Box<FxHashSet<ast::NodeId>>,
453 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
454 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
455 let should_warn = match item.node {
461 | hir::ItemStruct(..)
462 | hir::ItemUnion(..) => true,
465 let ctor_id = get_struct_ctor_id(item);
466 should_warn && !self.symbol_is_live(item.id, ctor_id)
469 fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
470 let field_type = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
471 let is_marker_field = match field_type.ty_to_def_id() {
472 Some(def_id) => self.tcx.lang_items().items().iter().any(|item| *item == Some(def_id)),
475 !field.is_positional()
476 && !self.symbol_is_live(field.id, None)
478 && !has_allow_dead_code_or_lang_attr(self.tcx, field.id, &field.attrs)
481 fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
482 !self.symbol_is_live(variant.data.id(), None)
483 && !has_allow_dead_code_or_lang_attr(self.tcx,
488 fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem) -> bool {
489 !self.symbol_is_live(fi.id, None)
490 && !has_allow_dead_code_or_lang_attr(self.tcx, fi.id, &fi.attrs)
493 // id := node id of an item's definition.
494 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
496 // If the item is a struct_ctor, then either its `id` or
497 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
498 // DefMap maps the ExprPath of a struct_ctor to the node referred by
499 // `ctor_id`. On the other hand, in a statement like
500 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
501 // DefMap maps <ty> to `id` instead.
502 fn symbol_is_live(&mut self,
504 ctor_id: Option<ast::NodeId>)
506 if self.live_symbols.contains(&id)
507 || ctor_id.map_or(false,
508 |ctor| self.live_symbols.contains(&ctor)) {
511 // If it's a type whose items are live, then it's live, too.
512 // This is done to handle the case where, for example, the static
513 // method of a private type is used, but the type itself is never
515 let def_id = self.tcx.hir.local_def_id(id);
516 let inherent_impls = self.tcx.inherent_impls(def_id);
517 for &impl_did in inherent_impls.iter() {
518 for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
519 if let Some(item_node_id) = self.tcx.hir.as_local_node_id(item_did) {
520 if self.live_symbols.contains(&item_node_id) {
529 fn warn_dead_code(&mut self,
531 span: syntax_pos::Span,
534 if !name.as_str().starts_with("_") {
536 .lint_node(lint::builtin::DEAD_CODE,
539 &format!("{} is never used: `{}`", node_type, name));
544 impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
545 /// Walk nested items in place so that we don't report dead-code
546 /// on inner functions when the outer function is already getting
547 /// an error. We could do this also by checking the parents, but
548 /// this is how the code is setup and it seems harmless enough.
549 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
550 NestedVisitorMap::All(&self.tcx.hir)
553 fn visit_item(&mut self, item: &'tcx hir::Item) {
554 if self.should_warn_about_item(item) {
559 item.node.descriptive_variant()
562 // Only continue if we didn't warn
563 intravisit::walk_item(self, item);
567 fn visit_variant(&mut self,
568 variant: &'tcx hir::Variant,
569 g: &'tcx hir::Generics,
571 if self.should_warn_about_variant(&variant.node) {
572 self.warn_dead_code(variant.node.data.id(), variant.span,
573 variant.node.name, "variant");
575 intravisit::walk_variant(self, variant, g, id);
579 fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem) {
580 if self.should_warn_about_foreign_item(fi) {
581 self.warn_dead_code(fi.id, fi.span, fi.name, fi.node.descriptive_variant());
583 intravisit::walk_foreign_item(self, fi);
586 fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
587 if self.should_warn_about_field(&field) {
588 self.warn_dead_code(field.id, field.span,
589 field.name, "field");
591 intravisit::walk_struct_field(self, field);
594 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
595 match impl_item.node {
596 hir::ImplItemKind::Const(_, body_id) => {
597 if !self.symbol_is_live(impl_item.id, None) {
598 self.warn_dead_code(impl_item.id, impl_item.span,
599 impl_item.name, "associated const");
601 self.visit_nested_body(body_id)
603 hir::ImplItemKind::Method(_, body_id) => {
604 if !self.symbol_is_live(impl_item.id, None) {
605 self.warn_dead_code(impl_item.id, impl_item.span,
606 impl_item.name, "method");
608 self.visit_nested_body(body_id)
610 hir::ImplItemKind::Type(..) => {}
614 // Overwrite so that we don't warn the trait item itself.
615 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
616 match trait_item.node {
617 hir::TraitItemKind::Const(_, Some(body_id)) |
618 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
619 self.visit_nested_body(body_id)
621 hir::TraitItemKind::Const(_, None) |
622 hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) |
623 hir::TraitItemKind::Type(..) => {}
628 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
629 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
630 let krate = tcx.hir.krate();
631 let live_symbols = find_live(tcx, access_levels, krate);
632 let mut visitor = DeadVisitor {
636 intravisit::walk_crate(&mut visitor, krate);