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.
16 use middle::{def, pat_util, privacy, ty};
18 use util::nodemap::NodeSet;
20 use std::collections::HashSet;
21 use syntax::{ast, codemap};
22 use syntax::ast_util::{local_def, is_local};
23 use syntax::attr::{self, AttrMetaMethods};
24 use syntax::visit::{self, Visitor};
26 // Any local node that may call something in its body block should be
27 // explored. For example, if it's a live NodeItem that is a
28 // function, then we should explore its block to check for codes that
29 // may need to be marked as live.
30 fn should_explore(tcx: &ty::ctxt, def_id: ast::DefId) -> bool {
31 if !is_local(def_id) {
35 match tcx.map.find(def_id.node) {
36 Some(ast_map::NodeItem(..))
37 | Some(ast_map::NodeImplItem(..))
38 | Some(ast_map::NodeForeignItem(..))
39 | Some(ast_map::NodeTraitItem(..)) => true,
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<ast::NodeId>,
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: ast::DefId) {
69 if should_explore(self.tcx, def_id) {
70 self.worklist.push(def_id.node);
72 self.live_symbols.insert(def_id.node);
75 fn lookup_and_handle_definition(&mut self, id: &ast::NodeId) {
76 use middle::ty::TypeVariants::{TyEnum, TyStruct};
78 // If `bar` is a trait item, make sure to mark Foo as alive in `Foo::bar`
79 self.tcx.tables.borrow().item_substs.get(id)
80 .and_then(|substs| substs.substs.self_ty())
81 .map(|ty| match ty.sty {
82 TyEnum(tyid, _) | TyStruct(tyid, _) => self.check_def_id(tyid.did),
86 self.tcx.def_map.borrow().get(id).map(|def| {
87 match def.full_def() {
88 def::DefConst(_) | def::DefAssociatedConst(..) => {
89 self.check_def_id(def.def_id())
91 _ if self.ignore_non_const_paths => (),
92 def::DefPrimTy(_) => (),
93 def::DefVariant(enum_id, variant_id, _) => {
94 self.check_def_id(enum_id);
95 if !self.ignore_variant_stack.contains(&variant_id.node) {
96 self.check_def_id(variant_id);
100 self.check_def_id(def.def_id());
106 fn lookup_and_handle_method(&mut self, id: ast::NodeId) {
107 let method_call = ty::MethodCall::expr(id);
108 let method = self.tcx.tables.borrow().method_map[&method_call];
109 self.check_def_id(method.def_id);
112 fn handle_field_access(&mut self, lhs: &ast::Expr, name: ast::Name) {
113 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
114 self.live_symbols.insert(def.struct_variant().field_named(name).did.node);
116 self.tcx.sess.span_bug(lhs.span, "named field access on non-struct")
120 fn handle_tup_field_access(&mut self, lhs: &ast::Expr, idx: usize) {
121 if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
122 self.live_symbols.insert(def.struct_variant().fields[idx].did.node);
126 fn handle_field_pattern_match(&mut self, lhs: &ast::Pat,
127 pats: &[codemap::Spanned<ast::FieldPat>]) {
128 let def = self.tcx.def_map.borrow().get(&lhs.id).unwrap().full_def();
129 let pat_ty = self.tcx.node_id_to_type(lhs.id);
130 let variant = match pat_ty.sty {
131 ty::TyStruct(adt, _) | ty::TyEnum(adt, _) => adt.variant_of_def(def),
132 _ => self.tcx.sess.span_bug(lhs.span, "non-ADT in struct pattern")
135 if let ast::PatWild(ast::PatWildSingle) = pat.node.pat.node {
138 self.live_symbols.insert(variant.field_named(pat.node.ident.name).did.node);
142 fn mark_live_symbols(&mut self) {
143 let mut scanned = HashSet::new();
144 while !self.worklist.is_empty() {
145 let id = self.worklist.pop().unwrap();
146 if scanned.contains(&id) {
151 match self.tcx.map.find(id) {
153 self.live_symbols.insert(id);
154 self.visit_node(node);
161 fn visit_node(&mut self, node: &ast_map::Node) {
162 let had_extern_repr = self.struct_has_extern_repr;
163 self.struct_has_extern_repr = false;
164 let had_inherited_pub_visibility = self.inherited_pub_visibility;
165 self.inherited_pub_visibility = false;
167 ast_map::NodeItem(item) => {
169 ast::ItemStruct(..) => {
170 self.struct_has_extern_repr = item.attrs.iter().any(|attr| {
171 attr::find_repr_attrs(self.tcx.sess.diagnostic(), attr)
172 .contains(&attr::ReprExtern)
175 visit::walk_item(self, &*item);
177 ast::ItemEnum(..) => {
178 self.inherited_pub_visibility = item.vis == ast::Public;
179 visit::walk_item(self, &*item);
183 | ast::ItemStatic(..)
184 | ast::ItemConst(..) => {
185 visit::walk_item(self, &*item);
190 ast_map::NodeTraitItem(trait_item) => {
191 visit::walk_trait_item(self, trait_item);
193 ast_map::NodeImplItem(impl_item) => {
194 visit::walk_impl_item(self, impl_item);
196 ast_map::NodeForeignItem(foreign_item) => {
197 visit::walk_foreign_item(self, &*foreign_item);
201 self.struct_has_extern_repr = had_extern_repr;
202 self.inherited_pub_visibility = had_inherited_pub_visibility;
206 impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
208 fn visit_struct_def(&mut self, def: &ast::StructDef, _: ast::Ident,
209 _: &ast::Generics, _: ast::NodeId) {
210 let has_extern_repr = self.struct_has_extern_repr;
211 let inherited_pub_visibility = self.inherited_pub_visibility;
212 let live_fields = def.fields.iter().filter(|f| {
213 has_extern_repr || inherited_pub_visibility || match f.node.kind {
214 ast::NamedField(_, ast::Public) => true,
218 self.live_symbols.extend(live_fields.map(|f| f.node.id));
220 visit::walk_struct_def(self, def);
223 fn visit_expr(&mut self, expr: &ast::Expr) {
225 ast::ExprMethodCall(..) => {
226 self.lookup_and_handle_method(expr.id);
228 ast::ExprField(ref lhs, ref ident) => {
229 self.handle_field_access(&**lhs, ident.node.name);
231 ast::ExprTupField(ref lhs, idx) => {
232 self.handle_tup_field_access(&**lhs, idx.node);
237 visit::walk_expr(self, expr);
240 fn visit_arm(&mut self, arm: &ast::Arm) {
241 if arm.pats.len() == 1 {
242 let pat = &*arm.pats[0];
243 let variants = pat_util::necessary_variants(&self.tcx.def_map, pat);
245 // Inside the body, ignore constructions of variants
246 // necessary for the pattern to match. Those construction sites
247 // can't be reached unless the variant is constructed elsewhere.
248 let len = self.ignore_variant_stack.len();
249 self.ignore_variant_stack.push_all(&*variants);
250 visit::walk_arm(self, arm);
251 self.ignore_variant_stack.truncate(len);
253 visit::walk_arm(self, arm);
257 fn visit_pat(&mut self, pat: &ast::Pat) {
258 let def_map = &self.tcx.def_map;
260 ast::PatStruct(_, ref fields, _) => {
261 self.handle_field_pattern_match(pat, fields);
263 _ if pat_util::pat_is_const(def_map, pat) => {
264 // it might be the only use of a const
265 self.lookup_and_handle_definition(&pat.id)
270 self.ignore_non_const_paths = true;
271 visit::walk_pat(self, pat);
272 self.ignore_non_const_paths = false;
275 fn visit_path(&mut self, path: &ast::Path, id: ast::NodeId) {
276 self.lookup_and_handle_definition(&id);
277 visit::walk_path(self, path);
280 fn visit_item(&mut self, _: &ast::Item) {
281 // Do not recurse into items. These items will be added to the
282 // worklist and recursed into manually if necessary.
286 fn has_allow_dead_code_or_lang_attr(attrs: &[ast::Attribute]) -> bool {
287 if attr::contains_name(attrs, "lang") {
291 let dead_code = lint::builtin::DEAD_CODE.name_lower();
292 for attr in lint::gather_attrs(attrs) {
294 Ok((ref name, lint::Allow, _))
295 if &name[..] == dead_code => return true,
302 // This visitor seeds items that
303 // 1) We want to explicitly consider as live:
304 // * Item annotated with #[allow(dead_code)]
305 // - This is done so that if we want to suppress warnings for a
306 // group of dead functions, we only have to annotate the "root".
307 // For example, if both `f` and `g` are dead and `f` calls `g`,
308 // then annotating `f` with `#[allow(dead_code)]` will suppress
309 // warning for both `f` and `g`.
310 // * Item annotated with #[lang=".."]
311 // - This is because lang items are always callable from elsewhere.
313 // 2) We are not sure to be live or not
314 // * Implementation of a trait method
316 worklist: Vec<ast::NodeId>
319 impl<'v> Visitor<'v> for LifeSeeder {
320 fn visit_item(&mut self, item: &ast::Item) {
321 let allow_dead_code = has_allow_dead_code_or_lang_attr(&item.attrs);
323 self.worklist.push(item.id);
326 ast::ItemEnum(ref enum_def, _) if allow_dead_code => {
327 self.worklist.extend(enum_def.variants.iter().map(|variant| variant.node.id));
329 ast::ItemTrait(_, _, _, ref trait_items) => {
330 for trait_item in trait_items {
331 match trait_item.node {
332 ast::ConstTraitItem(_, Some(_)) |
333 ast::MethodTraitItem(_, Some(_)) => {
334 if has_allow_dead_code_or_lang_attr(&trait_item.attrs) {
335 self.worklist.push(trait_item.id);
342 ast::ItemImpl(_, _, _, ref opt_trait, _, ref impl_items) => {
343 for impl_item in impl_items {
344 match impl_item.node {
345 ast::ConstImplItem(..) |
346 ast::MethodImplItem(..) => {
347 if opt_trait.is_some() ||
348 has_allow_dead_code_or_lang_attr(&impl_item.attrs) {
349 self.worklist.push(impl_item.id);
352 ast::TypeImplItem(_) => {}
353 ast::MacImplItem(_) => panic!("unexpanded macro")
359 visit::walk_item(self, item);
363 fn create_and_seed_worklist(tcx: &ty::ctxt,
364 exported_items: &privacy::ExportedItems,
365 reachable_symbols: &NodeSet,
366 krate: &ast::Crate) -> Vec<ast::NodeId> {
367 let mut worklist = Vec::new();
369 // Preferably, we would only need to seed the worklist with reachable
370 // symbols. However, since the set of reachable symbols differs
371 // depending on whether a crate is built as bin or lib, and we want
372 // the warning to be consistent, we also seed the worklist with
374 for id in exported_items {
377 for id in reachable_symbols {
378 // Reachable variants can be dead, because we warn about
379 // variants never constructed, not variants never used.
380 if let Some(ast_map::NodeVariant(..)) = tcx.map.find(*id) {
387 match *tcx.sess.entry_fn.borrow() {
388 Some((id, _)) => worklist.push(id),
392 // Seed implemented trait items
393 let mut life_seeder = LifeSeeder {
396 visit::walk_crate(&mut life_seeder, krate);
398 return life_seeder.worklist;
401 fn find_live(tcx: &ty::ctxt,
402 exported_items: &privacy::ExportedItems,
403 reachable_symbols: &NodeSet,
405 -> Box<HashSet<ast::NodeId>> {
406 let worklist = create_and_seed_worklist(tcx, exported_items,
407 reachable_symbols, krate);
408 let mut symbol_visitor = MarkSymbolVisitor::new(tcx, worklist);
409 symbol_visitor.mark_live_symbols();
410 symbol_visitor.live_symbols
413 fn get_struct_ctor_id(item: &ast::Item) -> Option<ast::NodeId> {
415 ast::ItemStruct(ref struct_def, _) => struct_def.ctor_id,
420 struct DeadVisitor<'a, 'tcx: 'a> {
421 tcx: &'a ty::ctxt<'tcx>,
422 live_symbols: Box<HashSet<ast::NodeId>>,
425 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
426 fn should_warn_about_item(&mut self, item: &ast::Item) -> bool {
427 let should_warn = match item.node {
432 | ast::ItemStruct(..) => true,
435 let ctor_id = get_struct_ctor_id(item);
436 should_warn && !self.symbol_is_live(item.id, ctor_id)
439 fn should_warn_about_field(&mut self, node: &ast::StructField_) -> bool {
440 let is_named = node.ident().is_some();
441 let field_type = self.tcx.node_id_to_type(node.id);
442 let is_marker_field = match field_type.ty_to_def_id() {
443 Some(def_id) => self.tcx.lang_items.items().any(|(_, item)| *item == Some(def_id)),
447 && !self.symbol_is_live(node.id, None)
449 && !has_allow_dead_code_or_lang_attr(&node.attrs)
452 fn should_warn_about_variant(&mut self, variant: &ast::Variant_) -> bool {
453 !self.symbol_is_live(variant.id, None)
454 && !has_allow_dead_code_or_lang_attr(&variant.attrs)
457 // id := node id of an item's definition.
458 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
460 // If the item is a struct_ctor, then either its `id` or
461 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
462 // DefMap maps the ExprPath of a struct_ctor to the node referred by
463 // `ctor_id`. On the other hand, in a statement like
464 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
465 // DefMap maps <ty> to `id` instead.
466 fn symbol_is_live(&mut self, id: ast::NodeId,
467 ctor_id: Option<ast::NodeId>) -> bool {
468 if self.live_symbols.contains(&id)
469 || ctor_id.map_or(false,
470 |ctor| self.live_symbols.contains(&ctor)) {
473 // If it's a type whose items are live, then it's live, too.
474 // This is done to handle the case where, for example, the static
475 // method of a private type is used, but the type itself is never
477 let impl_items = self.tcx.impl_items.borrow();
478 match self.tcx.inherent_impls.borrow().get(&local_def(id)) {
481 for impl_did in impl_list.iter() {
482 for item_did in impl_items.get(impl_did).unwrap().iter() {
483 if self.live_symbols.contains(&item_did.def_id()
494 fn warn_dead_code(&mut self,
499 let name = name.as_str();
500 if !name.starts_with("_") {
503 .add_lint(lint::builtin::DEAD_CODE,
506 format!("{} is never used: `{}`", node_type, name));
511 impl<'a, 'tcx, 'v> Visitor<'v> for DeadVisitor<'a, 'tcx> {
512 fn visit_item(&mut self, item: &ast::Item) {
513 if self.should_warn_about_item(item) {
518 item.node.descriptive_variant()
522 ast::ItemEnum(ref enum_def, _) => {
523 for variant in &enum_def.variants {
524 if self.should_warn_about_variant(&variant.node) {
525 self.warn_dead_code(variant.node.id, variant.span,
526 variant.node.name.name, "variant");
533 visit::walk_item(self, item);
536 fn visit_foreign_item(&mut self, fi: &ast::ForeignItem) {
537 if !self.symbol_is_live(fi.id, None) {
538 self.warn_dead_code(fi.id, fi.span, fi.ident.name, fi.node.descriptive_variant());
540 visit::walk_foreign_item(self, fi);
543 fn visit_struct_field(&mut self, field: &ast::StructField) {
544 if self.should_warn_about_field(&field.node) {
545 self.warn_dead_code(field.node.id, field.span,
546 field.node.ident().unwrap().name, "struct field");
549 visit::walk_struct_field(self, field);
552 fn visit_impl_item(&mut self, impl_item: &ast::ImplItem) {
553 match impl_item.node {
554 ast::ConstImplItem(_, ref expr) => {
555 if !self.symbol_is_live(impl_item.id, None) {
556 self.warn_dead_code(impl_item.id, impl_item.span,
557 impl_item.ident.name, "associated const");
559 visit::walk_expr(self, expr)
561 ast::MethodImplItem(_, ref body) => {
562 if !self.symbol_is_live(impl_item.id, None) {
563 self.warn_dead_code(impl_item.id, impl_item.span,
564 impl_item.ident.name, "method");
566 visit::walk_block(self, body)
568 ast::TypeImplItem(..) |
569 ast::MacImplItem(..) => {}
573 // Overwrite so that we don't warn the trait item itself.
574 fn visit_trait_item(&mut self, trait_item: &ast::TraitItem) {
575 match trait_item.node {
576 ast::ConstTraitItem(_, Some(ref expr)) => {
577 visit::walk_expr(self, expr)
579 ast::MethodTraitItem(_, Some(ref body)) => {
580 visit::walk_block(self, body)
582 ast::ConstTraitItem(_, None) |
583 ast::MethodTraitItem(_, None) |
584 ast::TypeTraitItem(..) => {}
589 pub fn check_crate(tcx: &ty::ctxt,
590 exported_items: &privacy::ExportedItems,
591 reachable_symbols: &NodeSet) {
592 let krate = tcx.map.krate();
593 let live_symbols = find_live(tcx, exported_items,
594 reachable_symbols, krate);
595 let mut visitor = DeadVisitor { tcx: tcx, live_symbols: live_symbols };
596 visit::walk_crate(&mut visitor, krate);