rust/src/librustc/middle/dead.rs
2016-08-17 06:32:00 +03:00

599 lines
22 KiB
Rust

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// This implements the dead-code warning pass. It follows middle::reachable
// closely. The idea is that all reachable symbols are live, codes called
// from live codes are live, and everything else is dead.
use dep_graph::DepNode;
use hir::map as ast_map;
use hir::{self, pat_util, PatKind};
use hir::intravisit::{self, Visitor};
use middle::privacy;
use ty::{self, TyCtxt};
use hir::def::Def;
use hir::def_id::{DefId};
use lint;
use std::collections::HashSet;
use syntax::{ast, codemap};
use syntax::attr;
use syntax_pos;
// Any local node that may call something in its body block should be
// explored. For example, if it's a live NodeItem that is a
// function, then we should explore its block to check for codes that
// may need to be marked as live.
fn should_explore<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
node_id: ast::NodeId) -> bool {
match tcx.map.find(node_id) {
Some(ast_map::NodeItem(..)) |
Some(ast_map::NodeImplItem(..)) |
Some(ast_map::NodeForeignItem(..)) |
Some(ast_map::NodeTraitItem(..)) =>
true,
_ =>
false
}
}
struct MarkSymbolVisitor<'a, 'tcx: 'a> {
worklist: Vec<ast::NodeId>,
tcx: TyCtxt<'a, 'tcx, 'tcx>,
live_symbols: Box<HashSet<ast::NodeId>>,
struct_has_extern_repr: bool,
ignore_non_const_paths: bool,
inherited_pub_visibility: bool,
ignore_variant_stack: Vec<DefId>,
}
impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
worklist: Vec<ast::NodeId>) -> MarkSymbolVisitor<'a, 'tcx> {
MarkSymbolVisitor {
worklist: worklist,
tcx: tcx,
live_symbols: box HashSet::new(),
struct_has_extern_repr: false,
ignore_non_const_paths: false,
inherited_pub_visibility: false,
ignore_variant_stack: vec![],
}
}
fn check_def_id(&mut self, def_id: DefId) {
if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
if should_explore(self.tcx, node_id) {
self.worklist.push(node_id);
}
self.live_symbols.insert(node_id);
}
}
fn insert_def_id(&mut self, def_id: DefId) {
if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
debug_assert!(!should_explore(self.tcx, node_id));
self.live_symbols.insert(node_id);
}
}
fn lookup_and_handle_definition(&mut self, id: ast::NodeId) {
use ty::TypeVariants::{TyEnum, TyStruct};
let def = self.tcx.expect_def(id);
// If `bar` is a trait item, make sure to mark Foo as alive in `Foo::bar`
match def {
Def::AssociatedTy(..) | Def::Method(_) | Def::AssociatedConst(_)
if self.tcx.trait_of_item(def.def_id()).is_some() => {
if let Some(substs) = self.tcx.tables.borrow().item_substs.get(&id) {
match substs.substs.types[0].sty {
TyEnum(tyid, _) | TyStruct(tyid, _) => {
self.check_def_id(tyid.did)
}
_ => {}
}
}
}
_ => {}
}
match def {
Def::Const(_) | Def::AssociatedConst(..) => {
self.check_def_id(def.def_id());
}
_ if self.ignore_non_const_paths => (),
Def::PrimTy(_) => (),
Def::SelfTy(..) => (),
Def::Variant(enum_id, variant_id) => {
self.check_def_id(enum_id);
if !self.ignore_variant_stack.contains(&variant_id) {
self.check_def_id(variant_id);
}
}
_ => {
self.check_def_id(def.def_id());
}
}
}
fn lookup_and_handle_method(&mut self, id: ast::NodeId) {
let method_call = ty::MethodCall::expr(id);
let method = self.tcx.tables.borrow().method_map[&method_call];
self.check_def_id(method.def_id);
}
fn handle_field_access(&mut self, lhs: &hir::Expr, name: ast::Name) {
if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
self.insert_def_id(def.struct_variant().field_named(name).did);
} else {
span_bug!(lhs.span, "named field access on non-struct")
}
}
fn handle_tup_field_access(&mut self, lhs: &hir::Expr, idx: usize) {
if let ty::TyStruct(def, _) = self.tcx.expr_ty_adjusted(lhs).sty {
self.insert_def_id(def.struct_variant().fields[idx].did);
}
}
fn handle_field_pattern_match(&mut self, lhs: &hir::Pat,
pats: &[codemap::Spanned<hir::FieldPat>]) {
let variant = match self.tcx.node_id_to_type(lhs.id).sty {
ty::TyStruct(adt, _) | ty::TyEnum(adt, _) => {
adt.variant_of_def(self.tcx.expect_def(lhs.id))
}
_ => span_bug!(lhs.span, "non-ADT in struct pattern")
};
for pat in pats {
if let PatKind::Wild = pat.node.pat.node {
continue;
}
self.insert_def_id(variant.field_named(pat.node.name).did);
}
}
fn mark_live_symbols(&mut self) {
let mut scanned = HashSet::new();
while !self.worklist.is_empty() {
let id = self.worklist.pop().unwrap();
if scanned.contains(&id) {
continue
}
scanned.insert(id);
if let Some(ref node) = self.tcx.map.find(id) {
self.live_symbols.insert(id);
self.visit_node(node);
}
}
}
fn visit_node(&mut self, node: &ast_map::Node) {
let had_extern_repr = self.struct_has_extern_repr;
self.struct_has_extern_repr = false;
let had_inherited_pub_visibility = self.inherited_pub_visibility;
self.inherited_pub_visibility = false;
match *node {
ast_map::NodeItem(item) => {
match item.node {
hir::ItemStruct(..) => {
self.struct_has_extern_repr = item.attrs.iter().any(|attr| {
attr::find_repr_attrs(self.tcx.sess.diagnostic(), attr)
.contains(&attr::ReprExtern)
});
intravisit::walk_item(self, &item);
}
hir::ItemEnum(..) => {
self.inherited_pub_visibility = item.vis == hir::Public;
intravisit::walk_item(self, &item);
}
hir::ItemFn(..)
| hir::ItemTy(..)
| hir::ItemStatic(..)
| hir::ItemConst(..) => {
intravisit::walk_item(self, &item);
}
_ => ()
}
}
ast_map::NodeTraitItem(trait_item) => {
intravisit::walk_trait_item(self, trait_item);
}
ast_map::NodeImplItem(impl_item) => {
intravisit::walk_impl_item(self, impl_item);
}
ast_map::NodeForeignItem(foreign_item) => {
intravisit::walk_foreign_item(self, &foreign_item);
}
_ => ()
}
self.struct_has_extern_repr = had_extern_repr;
self.inherited_pub_visibility = had_inherited_pub_visibility;
}
}
impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
fn visit_variant_data(&mut self, def: &hir::VariantData, _: ast::Name,
_: &hir::Generics, _: ast::NodeId, _: syntax_pos::Span) {
let has_extern_repr = self.struct_has_extern_repr;
let inherited_pub_visibility = self.inherited_pub_visibility;
let live_fields = def.fields().iter().filter(|f| {
has_extern_repr || inherited_pub_visibility || f.vis == hir::Public
});
self.live_symbols.extend(live_fields.map(|f| f.id));
intravisit::walk_struct_def(self, def);
}
fn visit_expr(&mut self, expr: &hir::Expr) {
match expr.node {
hir::ExprMethodCall(..) => {
self.lookup_and_handle_method(expr.id);
}
hir::ExprField(ref lhs, ref name) => {
self.handle_field_access(&lhs, name.node);
}
hir::ExprTupField(ref lhs, idx) => {
self.handle_tup_field_access(&lhs, idx.node);
}
_ => ()
}
intravisit::walk_expr(self, expr);
}
fn visit_arm(&mut self, arm: &hir::Arm) {
if arm.pats.len() == 1 {
let pat = &*arm.pats[0];
let variants = pat_util::necessary_variants(&self.tcx.def_map.borrow(), pat);
// Inside the body, ignore constructions of variants
// necessary for the pattern to match. Those construction sites
// can't be reached unless the variant is constructed elsewhere.
let len = self.ignore_variant_stack.len();
self.ignore_variant_stack.extend_from_slice(&variants);
intravisit::walk_arm(self, arm);
self.ignore_variant_stack.truncate(len);
} else {
intravisit::walk_arm(self, arm);
}
}
fn visit_pat(&mut self, pat: &hir::Pat) {
let def_map = &self.tcx.def_map;
match pat.node {
PatKind::Struct(_, ref fields, _) => {
self.handle_field_pattern_match(pat, fields);
}
_ if pat_util::pat_is_const(&def_map.borrow(), pat) => {
// it might be the only use of a const
self.lookup_and_handle_definition(pat.id)
}
_ => ()
}
self.ignore_non_const_paths = true;
intravisit::walk_pat(self, pat);
self.ignore_non_const_paths = false;
}
fn visit_path(&mut self, path: &hir::Path, id: ast::NodeId) {
self.lookup_and_handle_definition(id);
intravisit::walk_path(self, path);
}
fn visit_path_list_item(&mut self, path: &hir::Path, item: &hir::PathListItem) {
self.lookup_and_handle_definition(item.node.id());
intravisit::walk_path_list_item(self, path, item);
}
}
fn has_allow_dead_code_or_lang_attr(attrs: &[ast::Attribute]) -> bool {
if attr::contains_name(attrs, "lang") {
return true;
}
let dead_code = lint::builtin::DEAD_CODE.name_lower();
for attr in lint::gather_attrs(attrs) {
match attr {
Ok((ref name, lint::Allow, _))
if &name[..] == dead_code => return true,
_ => (),
}
}
false
}
// This visitor seeds items that
// 1) We want to explicitly consider as live:
// * Item annotated with #[allow(dead_code)]
// - This is done so that if we want to suppress warnings for a
// group of dead functions, we only have to annotate the "root".
// For example, if both `f` and `g` are dead and `f` calls `g`,
// then annotating `f` with `#[allow(dead_code)]` will suppress
// warning for both `f` and `g`.
// * Item annotated with #[lang=".."]
// - This is because lang items are always callable from elsewhere.
// or
// 2) We are not sure to be live or not
// * Implementation of a trait method
struct LifeSeeder {
worklist: Vec<ast::NodeId>
}
impl<'v> Visitor<'v> for LifeSeeder {
fn visit_item(&mut self, item: &hir::Item) {
let allow_dead_code = has_allow_dead_code_or_lang_attr(&item.attrs);
if allow_dead_code {
self.worklist.push(item.id);
}
match item.node {
hir::ItemEnum(ref enum_def, _) if allow_dead_code => {
self.worklist.extend(enum_def.variants.iter()
.map(|variant| variant.node.data.id()));
}
hir::ItemTrait(_, _, _, ref trait_items) => {
for trait_item in trait_items {
match trait_item.node {
hir::ConstTraitItem(_, Some(_)) |
hir::MethodTraitItem(_, Some(_)) => {
if has_allow_dead_code_or_lang_attr(&trait_item.attrs) {
self.worklist.push(trait_item.id);
}
}
_ => {}
}
}
}
hir::ItemImpl(_, _, _, ref opt_trait, _, ref impl_items) => {
for impl_item in impl_items {
if opt_trait.is_some() ||
has_allow_dead_code_or_lang_attr(&impl_item.attrs) {
self.worklist.push(impl_item.id);
}
}
}
_ => ()
}
}
}
fn create_and_seed_worklist<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
access_levels: &privacy::AccessLevels,
krate: &hir::Crate)
-> Vec<ast::NodeId> {
let mut worklist = Vec::new();
for (id, _) in &access_levels.map {
worklist.push(*id);
}
// Seed entry point
if let Some((id, _)) = *tcx.sess.entry_fn.borrow() {
worklist.push(id);
}
// Seed implemented trait items
let mut life_seeder = LifeSeeder {
worklist: worklist
};
krate.visit_all_items(&mut life_seeder);
return life_seeder.worklist;
}
fn find_live<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
access_levels: &privacy::AccessLevels,
krate: &hir::Crate)
-> Box<HashSet<ast::NodeId>> {
let worklist = create_and_seed_worklist(tcx, access_levels, krate);
let mut symbol_visitor = MarkSymbolVisitor::new(tcx, worklist);
symbol_visitor.mark_live_symbols();
symbol_visitor.live_symbols
}
fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
match item.node {
hir::ItemStruct(ref struct_def, _) if !struct_def.is_struct() => {
Some(struct_def.id())
}
_ => None
}
}
struct DeadVisitor<'a, 'tcx: 'a> {
tcx: TyCtxt<'a, 'tcx, 'tcx>,
live_symbols: Box<HashSet<ast::NodeId>>,
}
impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
let should_warn = match item.node {
hir::ItemStatic(..)
| hir::ItemConst(..)
| hir::ItemFn(..)
| hir::ItemEnum(..)
| hir::ItemStruct(..) => true,
_ => false
};
let ctor_id = get_struct_ctor_id(item);
should_warn && !self.symbol_is_live(item.id, ctor_id)
}
fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
let field_type = self.tcx.node_id_to_type(field.id);
let is_marker_field = match field_type.ty_to_def_id() {
Some(def_id) => self.tcx.lang_items.items().iter().any(|item| *item == Some(def_id)),
_ => false
};
!field.is_positional()
&& !self.symbol_is_live(field.id, None)
&& !is_marker_field
&& !has_allow_dead_code_or_lang_attr(&field.attrs)
}
fn should_warn_about_variant(&mut self, variant: &hir::Variant_) -> bool {
!self.symbol_is_live(variant.data.id(), None)
&& !has_allow_dead_code_or_lang_attr(&variant.attrs)
}
// id := node id of an item's definition.
// ctor_id := `Some` if the item is a struct_ctor (tuple struct),
// `None` otherwise.
// If the item is a struct_ctor, then either its `id` or
// `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
// DefMap maps the ExprPath of a struct_ctor to the node referred by
// `ctor_id`. On the other hand, in a statement like
// `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
// DefMap maps <ty> to `id` instead.
fn symbol_is_live(&mut self,
id: ast::NodeId,
ctor_id: Option<ast::NodeId>)
-> bool {
if self.live_symbols.contains(&id)
|| ctor_id.map_or(false,
|ctor| self.live_symbols.contains(&ctor)) {
return true;
}
// If it's a type whose items are live, then it's live, too.
// This is done to handle the case where, for example, the static
// method of a private type is used, but the type itself is never
// called directly.
let impl_items = self.tcx.impl_items.borrow();
if let Some(impl_list) =
self.tcx.inherent_impls.borrow().get(&self.tcx.map.local_def_id(id)) {
for impl_did in impl_list.iter() {
for item_did in impl_items.get(impl_did).unwrap().iter() {
if let Some(item_node_id) =
self.tcx.map.as_local_node_id(item_did.def_id()) {
if self.live_symbols.contains(&item_node_id) {
return true;
}
}
}
}
}
false
}
fn warn_dead_code(&mut self,
id: ast::NodeId,
span: syntax_pos::Span,
name: ast::Name,
node_type: &str) {
let name = name.as_str();
if !name.starts_with("_") {
self.tcx
.sess
.add_lint(lint::builtin::DEAD_CODE,
id,
span,
format!("{} is never used: `{}`", node_type, name));
}
}
}
impl<'a, 'tcx, 'v> Visitor<'v> for DeadVisitor<'a, 'tcx> {
/// Walk nested items in place so that we don't report dead-code
/// on inner functions when the outer function is already getting
/// an error. We could do this also by checking the parents, but
/// this is how the code is setup and it seems harmless enough.
fn visit_nested_item(&mut self, item: hir::ItemId) {
let tcx = self.tcx;
self.visit_item(tcx.map.expect_item(item.id))
}
fn visit_item(&mut self, item: &hir::Item) {
if self.should_warn_about_item(item) {
self.warn_dead_code(
item.id,
item.span,
item.name,
item.node.descriptive_variant()
);
} else {
// Only continue if we didn't warn
intravisit::walk_item(self, item);
}
}
fn visit_variant(&mut self, variant: &hir::Variant, g: &hir::Generics, id: ast::NodeId) {
if self.should_warn_about_variant(&variant.node) {
self.warn_dead_code(variant.node.data.id(), variant.span,
variant.node.name, "variant");
} else {
intravisit::walk_variant(self, variant, g, id);
}
}
fn visit_foreign_item(&mut self, fi: &hir::ForeignItem) {
if !self.symbol_is_live(fi.id, None) {
self.warn_dead_code(fi.id, fi.span, fi.name, fi.node.descriptive_variant());
}
intravisit::walk_foreign_item(self, fi);
}
fn visit_struct_field(&mut self, field: &hir::StructField) {
if self.should_warn_about_field(&field) {
self.warn_dead_code(field.id, field.span,
field.name, "struct field");
}
intravisit::walk_struct_field(self, field);
}
fn visit_impl_item(&mut self, impl_item: &hir::ImplItem) {
match impl_item.node {
hir::ImplItemKind::Const(_, ref expr) => {
if !self.symbol_is_live(impl_item.id, None) {
self.warn_dead_code(impl_item.id, impl_item.span,
impl_item.name, "associated const");
}
intravisit::walk_expr(self, expr)
}
hir::ImplItemKind::Method(_, ref body) => {
if !self.symbol_is_live(impl_item.id, None) {
self.warn_dead_code(impl_item.id, impl_item.span,
impl_item.name, "method");
}
intravisit::walk_block(self, body)
}
hir::ImplItemKind::Type(..) => {}
}
}
// Overwrite so that we don't warn the trait item itself.
fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
match trait_item.node {
hir::ConstTraitItem(_, Some(ref expr)) => {
intravisit::walk_expr(self, expr)
}
hir::MethodTraitItem(_, Some(ref body)) => {
intravisit::walk_block(self, body)
}
hir::ConstTraitItem(_, None) |
hir::MethodTraitItem(_, None) |
hir::TypeTraitItem(..) => {}
}
}
}
pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
access_levels: &privacy::AccessLevels) {
let _task = tcx.dep_graph.in_task(DepNode::DeadCheck);
let krate = tcx.map.krate();
let live_symbols = find_live(tcx, access_levels, krate);
let mut visitor = DeadVisitor { tcx: tcx, live_symbols: live_symbols };
intravisit::walk_crate(&mut visitor, krate);
}