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, 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 repr_has_repr_c: 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(..) | Def::TyAlias(_) => {
79 self.check_def_id(def.def_id());
81 _ if self.in_pat => (),
82 Def::PrimTy(..) | Def::SelfTy(..) |
83 Def::Local(..) | Def::Upvar(..) => {}
84 Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
85 if let Some(enum_id) = self.tcx.parent_def_id(variant_id) {
86 self.check_def_id(enum_id);
88 if !self.ignore_variant_stack.contains(&variant_id) {
89 self.check_def_id(variant_id);
93 self.check_def_id(def.def_id());
98 fn lookup_and_handle_method(&mut self, id: hir::HirId) {
99 if let Some(def) = self.tables.type_dependent_defs().get(id) {
100 self.check_def_id(def.def_id());
102 bug!("no type-dependent def for method");
106 fn handle_field_access(&mut self, lhs: &hir::Expr, node_id: ast::NodeId) {
107 match self.tables.expr_ty_adjusted(lhs).sty {
108 ty::TyAdt(def, _) => {
109 let index = self.tcx.field_index(node_id, self.tables);
110 self.insert_def_id(def.non_enum_variant().fields[index].did);
112 ty::TyTuple(..) => {}
113 _ => span_bug!(lhs.span, "named field access on non-ADT"),
117 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat, def: Def,
118 pats: &[codemap::Spanned<hir::FieldPat>]) {
119 let variant = match self.tables.node_id_to_type(lhs.hir_id).sty {
120 ty::TyAdt(adt, _) => adt.variant_of_def(def),
121 _ => span_bug!(lhs.span, "non-ADT in struct pattern")
124 if let PatKind::Wild = pat.node.pat.node {
127 let index = self.tcx.field_index(pat.node.id, self.tables);
128 self.insert_def_id(variant.fields[index].did);
132 fn mark_live_symbols(&mut self) {
133 let mut scanned = FxHashSet();
134 while !self.worklist.is_empty() {
135 let id = self.worklist.pop().unwrap();
136 if scanned.contains(&id) {
141 if let Some(ref node) = self.tcx.hir.find(id) {
142 self.live_symbols.insert(id);
143 self.visit_node(node);
148 fn visit_node(&mut self, node: &hir_map::Node<'tcx>) {
149 let had_repr_c = self.repr_has_repr_c;
150 self.repr_has_repr_c = false;
151 let had_inherited_pub_visibility = self.inherited_pub_visibility;
152 self.inherited_pub_visibility = false;
154 hir_map::NodeItem(item) => {
156 hir::ItemStruct(..) | hir::ItemUnion(..) => {
157 let def_id = self.tcx.hir.local_def_id(item.id);
158 let def = self.tcx.adt_def(def_id);
159 self.repr_has_repr_c = def.repr.c();
161 intravisit::walk_item(self, &item);
163 hir::ItemEnum(..) => {
164 self.inherited_pub_visibility = item.vis.node.is_pub();
165 intravisit::walk_item(self, &item);
169 | hir::ItemStatic(..)
170 | hir::ItemConst(..) => {
171 intravisit::walk_item(self, &item);
176 hir_map::NodeTraitItem(trait_item) => {
177 intravisit::walk_trait_item(self, trait_item);
179 hir_map::NodeImplItem(impl_item) => {
180 intravisit::walk_impl_item(self, impl_item);
182 hir_map::NodeForeignItem(foreign_item) => {
183 intravisit::walk_foreign_item(self, &foreign_item);
187 self.repr_has_repr_c = had_repr_c;
188 self.inherited_pub_visibility = had_inherited_pub_visibility;
191 fn mark_as_used_if_union(&mut self, adt: &ty::AdtDef, fields: &hir::HirVec<hir::Field>) {
192 if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did.is_local() {
193 for field in fields {
194 let index = self.tcx.field_index(field.id, self.tables);
195 self.insert_def_id(adt.non_enum_variant().fields[index].did);
201 impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
202 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
203 NestedVisitorMap::None
206 fn visit_nested_body(&mut self, body: hir::BodyId) {
207 let old_tables = self.tables;
208 self.tables = self.tcx.body_tables(body);
209 let body = self.tcx.hir.body(body);
210 self.visit_body(body);
211 self.tables = old_tables;
214 fn visit_variant_data(&mut self, def: &'tcx hir::VariantData, _: ast::Name,
215 _: &hir::Generics, _: ast::NodeId, _: syntax_pos::Span) {
216 let has_repr_c = self.repr_has_repr_c;
217 let inherited_pub_visibility = self.inherited_pub_visibility;
218 let live_fields = def.fields().iter().filter(|f| {
219 has_repr_c || inherited_pub_visibility || f.vis.node.is_pub()
221 self.live_symbols.extend(live_fields.map(|f| f.id));
223 intravisit::walk_struct_def(self, def);
226 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
228 hir::ExprPath(ref qpath @ hir::QPath::TypeRelative(..)) => {
229 let def = self.tables.qpath_def(qpath, expr.hir_id);
230 self.handle_definition(def);
232 hir::ExprMethodCall(..) => {
233 self.lookup_and_handle_method(expr.hir_id);
235 hir::ExprField(ref lhs, ..) => {
236 self.handle_field_access(&lhs, expr.id);
238 hir::ExprStruct(_, ref fields, _) => {
239 if let ty::TypeVariants::TyAdt(ref adt, _) = self.tables.expr_ty(expr).sty {
240 self.mark_as_used_if_union(adt, fields);
246 intravisit::walk_expr(self, expr);
249 fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
250 if arm.pats.len() == 1 {
251 let variants = arm.pats[0].necessary_variants();
253 // Inside the body, ignore constructions of variants
254 // necessary for the pattern to match. Those construction sites
255 // can't be reached unless the variant is constructed elsewhere.
256 let len = self.ignore_variant_stack.len();
257 self.ignore_variant_stack.extend_from_slice(&variants);
258 intravisit::walk_arm(self, arm);
259 self.ignore_variant_stack.truncate(len);
261 intravisit::walk_arm(self, arm);
265 fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
267 PatKind::Struct(hir::QPath::Resolved(_, ref path), ref fields, _) => {
268 self.handle_field_pattern_match(pat, path.def, fields);
270 PatKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
271 let def = self.tables.qpath_def(qpath, pat.hir_id);
272 self.handle_definition(def);
278 intravisit::walk_pat(self, pat);
282 fn visit_path(&mut self, path: &'tcx hir::Path, _: ast::NodeId) {
283 self.handle_definition(path.def);
284 intravisit::walk_path(self, path);
288 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt,
290 attrs: &[ast::Attribute]) -> bool {
291 if attr::contains_name(attrs, "lang") || attr::contains_name(attrs, "panic_implementation") {
295 // #[used] also keeps the item alive forcefully,
296 // e.g. for placing it in a specific section.
297 if attr::contains_name(attrs, "used") {
301 // Don't lint about global allocators
302 if attr::contains_name(attrs, "global_allocator") {
306 // These constants are special for wasm
307 if attr::contains_name(attrs, "wasm_custom_section") {
311 tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
314 // This visitor seeds items that
315 // 1) We want to explicitly consider as live:
316 // * Item annotated with #[allow(dead_code)]
317 // - This is done so that if we want to suppress warnings for a
318 // group of dead functions, we only have to annotate the "root".
319 // For example, if both `f` and `g` are dead and `f` calls `g`,
320 // then annotating `f` with `#[allow(dead_code)]` will suppress
321 // warning for both `f` and `g`.
322 // * Item annotated with #[lang=".."]
323 // - This is because lang items are always callable from elsewhere.
325 // 2) We are not sure to be live or not
326 // * Implementation of a trait method
327 struct LifeSeeder<'k, 'tcx: 'k> {
328 worklist: Vec<ast::NodeId>,
329 krate: &'k hir::Crate,
330 tcx: TyCtxt<'k, 'tcx, 'tcx>,
333 impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
334 fn visit_item(&mut self, item: &hir::Item) {
335 let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx,
339 self.worklist.push(item.id);
342 hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
343 self.worklist.extend(enum_def.variants.iter()
344 .map(|variant| variant.node.data.id()));
346 hir::ItemTrait(.., ref trait_item_refs) => {
347 for trait_item_ref in trait_item_refs {
348 let trait_item = self.krate.trait_item(trait_item_ref.id);
349 match trait_item.node {
350 hir::TraitItemKind::Const(_, Some(_)) |
351 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
352 if has_allow_dead_code_or_lang_attr(self.tcx,
355 self.worklist.push(trait_item.id);
362 hir::ItemImpl(.., ref opt_trait, _, ref impl_item_refs) => {
363 for impl_item_ref in impl_item_refs {
364 let impl_item = self.krate.impl_item(impl_item_ref.id);
365 if opt_trait.is_some() ||
366 has_allow_dead_code_or_lang_attr(self.tcx,
369 self.worklist.push(impl_item_ref.id.node_id);
377 fn visit_trait_item(&mut self, _item: &hir::TraitItem) {
378 // ignore: we are handling this in `visit_item` above
381 fn visit_impl_item(&mut self, _item: &hir::ImplItem) {
382 // ignore: we are handling this in `visit_item` above
386 fn create_and_seed_worklist<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
387 access_levels: &privacy::AccessLevels,
389 -> Vec<ast::NodeId> {
390 let mut worklist = Vec::new();
391 for (id, _) in &access_levels.map {
396 if let Some((id, _, _)) = *tcx.sess.entry_fn.borrow() {
400 // Seed implemented trait items
401 let mut life_seeder = LifeSeeder {
406 krate.visit_all_item_likes(&mut life_seeder);
408 return life_seeder.worklist;
411 fn find_live<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
412 access_levels: &privacy::AccessLevels,
414 -> Box<FxHashSet<ast::NodeId>> {
415 let worklist = create_and_seed_worklist(tcx, access_levels, krate);
416 let mut symbol_visitor = MarkSymbolVisitor {
419 tables: &ty::TypeckTables::empty(None),
420 live_symbols: box FxHashSet(),
421 repr_has_repr_c: false,
423 inherited_pub_visibility: false,
424 ignore_variant_stack: vec![],
426 symbol_visitor.mark_live_symbols();
427 symbol_visitor.live_symbols
430 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
432 hir::ItemStruct(ref struct_def, _) if !struct_def.is_struct() => {
433 Some(struct_def.id())
439 struct DeadVisitor<'a, 'tcx: 'a> {
440 tcx: TyCtxt<'a, 'tcx, 'tcx>,
441 live_symbols: Box<FxHashSet<ast::NodeId>>,
444 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
445 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
446 let should_warn = match item.node {
452 | hir::ItemStruct(..)
453 | hir::ItemUnion(..) => true,
456 let ctor_id = get_struct_ctor_id(item);
457 should_warn && !self.symbol_is_live(item.id, ctor_id)
460 fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
461 let field_type = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
462 let is_marker_field = match field_type.ty_to_def_id() {
463 Some(def_id) => self.tcx.lang_items().items().iter().any(|item| *item == Some(def_id)),
466 !field.is_positional()
467 && !self.symbol_is_live(field.id, None)
469 && !has_allow_dead_code_or_lang_attr(self.tcx, field.id, &field.attrs)
472 fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
473 !self.symbol_is_live(variant.data.id(), None)
474 && !has_allow_dead_code_or_lang_attr(self.tcx,
479 fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem) -> bool {
480 !self.symbol_is_live(fi.id, None)
481 && !has_allow_dead_code_or_lang_attr(self.tcx, fi.id, &fi.attrs)
484 // id := node id of an item's definition.
485 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
487 // If the item is a struct_ctor, then either its `id` or
488 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
489 // DefMap maps the ExprPath of a struct_ctor to the node referred by
490 // `ctor_id`. On the other hand, in a statement like
491 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
492 // DefMap maps <ty> to `id` instead.
493 fn symbol_is_live(&mut self,
495 ctor_id: Option<ast::NodeId>)
497 if self.live_symbols.contains(&id)
498 || ctor_id.map_or(false,
499 |ctor| self.live_symbols.contains(&ctor)) {
502 // If it's a type whose items are live, then it's live, too.
503 // This is done to handle the case where, for example, the static
504 // method of a private type is used, but the type itself is never
506 let def_id = self.tcx.hir.local_def_id(id);
507 let inherent_impls = self.tcx.inherent_impls(def_id);
508 for &impl_did in inherent_impls.iter() {
509 for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
510 if let Some(item_node_id) = self.tcx.hir.as_local_node_id(item_did) {
511 if self.live_symbols.contains(&item_node_id) {
520 fn warn_dead_code(&mut self,
522 span: syntax_pos::Span,
526 if !name.as_str().starts_with("_") {
528 .lint_node(lint::builtin::DEAD_CODE,
531 &format!("{} is never {}: `{}`",
532 node_type, participle, name));
537 impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
538 /// Walk nested items in place so that we don't report dead-code
539 /// on inner functions when the outer function is already getting
540 /// an error. We could do this also by checking the parents, but
541 /// this is how the code is setup and it seems harmless enough.
542 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
543 NestedVisitorMap::All(&self.tcx.hir)
546 fn visit_item(&mut self, item: &'tcx hir::Item) {
547 if self.should_warn_about_item(item) {
548 // For items that have a definition with a signature followed by a
549 // block, point only at the signature.
550 let span = match item.node {
554 hir::ItemStruct(..) |
557 hir::ItemImpl(..) => self.tcx.sess.codemap().def_span(item.span),
564 item.node.descriptive_variant(),
568 // Only continue if we didn't warn
569 intravisit::walk_item(self, item);
573 fn visit_variant(&mut self,
574 variant: &'tcx hir::Variant,
575 g: &'tcx hir::Generics,
577 if self.should_warn_about_variant(&variant.node) {
578 self.warn_dead_code(variant.node.data.id(), variant.span, variant.node.name,
579 "variant", "constructed");
581 intravisit::walk_variant(self, variant, g, id);
585 fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem) {
586 if self.should_warn_about_foreign_item(fi) {
587 self.warn_dead_code(fi.id, fi.span, fi.name,
588 fi.node.descriptive_variant(), "used");
590 intravisit::walk_foreign_item(self, fi);
593 fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
594 if self.should_warn_about_field(&field) {
595 self.warn_dead_code(field.id, field.span, field.ident.name, "field", "used");
597 intravisit::walk_struct_field(self, field);
600 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
601 match impl_item.node {
602 hir::ImplItemKind::Const(_, body_id) => {
603 if !self.symbol_is_live(impl_item.id, None) {
604 self.warn_dead_code(impl_item.id,
606 impl_item.ident.name,
610 self.visit_nested_body(body_id)
612 hir::ImplItemKind::Method(_, body_id) => {
613 if !self.symbol_is_live(impl_item.id, None) {
614 let span = self.tcx.sess.codemap().def_span(impl_item.span);
615 self.warn_dead_code(impl_item.id, span, impl_item.ident.name, "method", "used");
617 self.visit_nested_body(body_id)
619 hir::ImplItemKind::Type(..) => {}
623 // Overwrite so that we don't warn the trait item itself.
624 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
625 match trait_item.node {
626 hir::TraitItemKind::Const(_, Some(body_id)) |
627 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
628 self.visit_nested_body(body_id)
630 hir::TraitItemKind::Const(_, None) |
631 hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) |
632 hir::TraitItemKind::Type(..) => {}
637 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
638 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
639 let krate = tcx.hir.krate();
640 let live_symbols = find_live(tcx, access_levels, krate);
641 let mut visitor = DeadVisitor {
645 intravisit::walk_crate(&mut visitor, krate);