668 lines
24 KiB
Rust
668 lines
24 KiB
Rust
// This implements the dead-code warning pass. It follows middle::reachable
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// closely. The idea is that all reachable symbols are live, codes called
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// from live codes are live, and everything else is dead.
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use crate::hir::Node;
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use crate::hir::{self, PatKind, TyKind};
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use crate::hir::intravisit::{self, Visitor, NestedVisitorMap};
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use crate::hir::itemlikevisit::ItemLikeVisitor;
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use crate::hir::def::{CtorOf, Res, DefKind};
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use crate::hir::CodegenFnAttrFlags;
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use crate::hir::def_id::{DefId, LOCAL_CRATE};
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use crate::lint;
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use crate::middle::privacy;
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use crate::ty::{self, DefIdTree, TyCtxt};
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use crate::util::nodemap::FxHashSet;
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use rustc_data_structures::fx::FxHashMap;
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use syntax::{ast, attr};
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use syntax::symbol::sym;
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use syntax_pos;
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// Any local node that may call something in its body block should be
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// explored. For example, if it's a live Node::Item that is a
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// function, then we should explore its block to check for codes that
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// may need to be marked as live.
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fn should_explore(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
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match tcx.hir().find(hir_id) {
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Some(Node::Item(..)) |
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Some(Node::ImplItem(..)) |
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Some(Node::ForeignItem(..)) |
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Some(Node::TraitItem(..)) =>
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true,
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_ =>
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false
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}
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}
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struct MarkSymbolVisitor<'a, 'tcx> {
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worklist: Vec<hir::HirId>,
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tcx: TyCtxt<'tcx>,
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tables: &'a ty::TypeckTables<'tcx>,
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live_symbols: FxHashSet<hir::HirId>,
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repr_has_repr_c: bool,
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in_pat: bool,
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inherited_pub_visibility: bool,
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ignore_variant_stack: Vec<DefId>,
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// maps from tuple struct constructors to tuple struct items
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struct_constructors: FxHashMap<hir::HirId, hir::HirId>,
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}
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impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
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fn check_def_id(&mut self, def_id: DefId) {
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if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
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if should_explore(self.tcx, hir_id) || self.struct_constructors.contains_key(&hir_id) {
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self.worklist.push(hir_id);
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}
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self.live_symbols.insert(hir_id);
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}
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}
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fn insert_def_id(&mut self, def_id: DefId) {
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if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
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debug_assert!(!should_explore(self.tcx, hir_id));
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self.live_symbols.insert(hir_id);
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}
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}
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fn handle_res(&mut self, res: Res) {
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match res {
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Res::Def(DefKind::Const, _)
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| Res::Def(DefKind::AssocConst, _)
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| Res::Def(DefKind::TyAlias, _) => {
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self.check_def_id(res.def_id());
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}
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_ if self.in_pat => {},
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Res::PrimTy(..) | Res::SelfTy(..) | Res::SelfCtor(..) |
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Res::Local(..) => {}
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Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => {
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let variant_id = self.tcx.parent(ctor_def_id).unwrap();
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let enum_id = self.tcx.parent(variant_id).unwrap();
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self.check_def_id(enum_id);
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if !self.ignore_variant_stack.contains(&ctor_def_id) {
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self.check_def_id(variant_id);
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}
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}
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Res::Def(DefKind::Variant, variant_id) => {
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let enum_id = self.tcx.parent(variant_id).unwrap();
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self.check_def_id(enum_id);
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if !self.ignore_variant_stack.contains(&variant_id) {
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self.check_def_id(variant_id);
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}
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}
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Res::ToolMod | Res::NonMacroAttr(..) | Res::Err => {}
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_ => {
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self.check_def_id(res.def_id());
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}
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}
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}
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fn lookup_and_handle_method(&mut self, id: hir::HirId) {
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if let Some(def_id) = self.tables.type_dependent_def_id(id) {
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self.check_def_id(def_id);
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} else {
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bug!("no type-dependent def for method");
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}
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}
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fn handle_field_access(&mut self, lhs: &hir::Expr, hir_id: hir::HirId) {
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match self.tables.expr_ty_adjusted(lhs).sty {
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ty::Adt(def, _) => {
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let index = self.tcx.field_index(hir_id, self.tables);
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self.insert_def_id(def.non_enum_variant().fields[index].did);
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}
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ty::Tuple(..) => {}
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_ => span_bug!(lhs.span, "named field access on non-ADT"),
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}
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}
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fn handle_field_pattern_match(&mut self, lhs: &hir::Pat, res: Res, pats: &[hir::FieldPat]) {
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let variant = match self.tables.node_type(lhs.hir_id).sty {
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ty::Adt(adt, _) => adt.variant_of_res(res),
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_ => span_bug!(lhs.span, "non-ADT in struct pattern")
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};
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for pat in pats {
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if let PatKind::Wild = pat.pat.node {
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continue;
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}
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let index = self.tcx.field_index(pat.hir_id, self.tables);
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self.insert_def_id(variant.fields[index].did);
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}
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}
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fn mark_live_symbols(&mut self) {
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let mut scanned = FxHashSet::default();
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while let Some(id) = self.worklist.pop() {
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if !scanned.insert(id) {
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continue
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}
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// in the case of tuple struct constructors we want to check the item, not the generated
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// tuple struct constructor function
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let id = self.struct_constructors.get(&id).cloned().unwrap_or(id);
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if let Some(node) = self.tcx.hir().find(id) {
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self.live_symbols.insert(id);
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self.visit_node(node);
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}
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}
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}
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fn visit_node(&mut self, node: Node<'tcx>) {
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let had_repr_c = self.repr_has_repr_c;
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self.repr_has_repr_c = false;
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let had_inherited_pub_visibility = self.inherited_pub_visibility;
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self.inherited_pub_visibility = false;
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match node {
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Node::Item(item) => {
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match item.node {
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hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
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let def_id = self.tcx.hir().local_def_id(item.hir_id);
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let def = self.tcx.adt_def(def_id);
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self.repr_has_repr_c = def.repr.c();
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intravisit::walk_item(self, &item);
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}
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hir::ItemKind::Enum(..) => {
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self.inherited_pub_visibility = item.vis.node.is_pub();
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intravisit::walk_item(self, &item);
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}
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hir::ItemKind::ForeignMod(..) => {}
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_ => {
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intravisit::walk_item(self, &item);
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}
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}
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}
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Node::TraitItem(trait_item) => {
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intravisit::walk_trait_item(self, trait_item);
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}
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Node::ImplItem(impl_item) => {
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intravisit::walk_impl_item(self, impl_item);
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}
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Node::ForeignItem(foreign_item) => {
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intravisit::walk_foreign_item(self, &foreign_item);
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}
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_ => {}
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}
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self.repr_has_repr_c = had_repr_c;
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self.inherited_pub_visibility = had_inherited_pub_visibility;
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}
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fn mark_as_used_if_union(&mut self, adt: &ty::AdtDef, fields: &hir::HirVec<hir::Field>) {
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if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did.is_local() {
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for field in fields {
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let index = self.tcx.field_index(field.hir_id, self.tables);
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self.insert_def_id(adt.non_enum_variant().fields[index].did);
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}
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}
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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NestedVisitorMap::None
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}
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fn visit_nested_body(&mut self, body: hir::BodyId) {
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let old_tables = self.tables;
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self.tables = self.tcx.body_tables(body);
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let body = self.tcx.hir().body(body);
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self.visit_body(body);
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self.tables = old_tables;
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}
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fn visit_variant_data(&mut self, def: &'tcx hir::VariantData, _: ast::Name,
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_: &hir::Generics, _: hir::HirId, _: syntax_pos::Span) {
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let has_repr_c = self.repr_has_repr_c;
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let inherited_pub_visibility = self.inherited_pub_visibility;
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let live_fields = def.fields().iter().filter(|f| {
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has_repr_c || inherited_pub_visibility || f.vis.node.is_pub()
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});
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self.live_symbols.extend(live_fields.map(|f| f.hir_id));
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intravisit::walk_struct_def(self, def);
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}
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fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
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match expr.node {
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hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
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let res = self.tables.qpath_res(qpath, expr.hir_id);
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self.handle_res(res);
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}
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hir::ExprKind::MethodCall(..) => {
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self.lookup_and_handle_method(expr.hir_id);
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}
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hir::ExprKind::Field(ref lhs, ..) => {
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self.handle_field_access(&lhs, expr.hir_id);
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}
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hir::ExprKind::Struct(_, ref fields, _) => {
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if let ty::Adt(ref adt, _) = self.tables.expr_ty(expr).sty {
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self.mark_as_used_if_union(adt, fields);
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}
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}
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_ => ()
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}
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intravisit::walk_expr(self, expr);
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}
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fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
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if arm.pats.len() == 1 {
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let variants = arm.pats[0].necessary_variants();
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// Inside the body, ignore constructions of variants
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// necessary for the pattern to match. Those construction sites
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// can't be reached unless the variant is constructed elsewhere.
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let len = self.ignore_variant_stack.len();
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self.ignore_variant_stack.extend_from_slice(&variants);
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intravisit::walk_arm(self, arm);
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self.ignore_variant_stack.truncate(len);
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} else {
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intravisit::walk_arm(self, arm);
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}
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}
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fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
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match pat.node {
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PatKind::Struct(ref path, ref fields, _) => {
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let res = self.tables.qpath_res(path, pat.hir_id);
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self.handle_field_pattern_match(pat, res, fields);
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}
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PatKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
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let res = self.tables.qpath_res(qpath, pat.hir_id);
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self.handle_res(res);
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}
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_ => ()
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}
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self.in_pat = true;
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intravisit::walk_pat(self, pat);
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self.in_pat = false;
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}
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fn visit_path(&mut self, path: &'tcx hir::Path, _: hir::HirId) {
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self.handle_res(path.res);
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intravisit::walk_path(self, path);
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}
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fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
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match ty.node {
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TyKind::Def(item_id, _) => {
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let item = self.tcx.hir().expect_item(item_id.id);
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intravisit::walk_item(self, item);
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}
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_ => ()
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}
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intravisit::walk_ty(self, ty);
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}
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}
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fn has_allow_dead_code_or_lang_attr(
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tcx: TyCtxt<'_>,
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id: hir::HirId,
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attrs: &[ast::Attribute],
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) -> bool {
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if attr::contains_name(attrs, sym::lang) {
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return true;
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}
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// Stable attribute for #[lang = "panic_impl"]
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if attr::contains_name(attrs, sym::panic_handler) {
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return true;
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}
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// (To be) stable attribute for #[lang = "oom"]
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if attr::contains_name(attrs, sym::alloc_error_handler) {
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return true;
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}
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let def_id = tcx.hir().local_def_id(id);
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let cg_attrs = tcx.codegen_fn_attrs(def_id);
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// #[used], #[no_mangle], #[export_name], etc also keeps the item alive
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// forcefully, e.g., for placing it in a specific section.
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if cg_attrs.contains_extern_indicator() ||
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cg_attrs.flags.contains(CodegenFnAttrFlags::USED) {
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return true;
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}
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tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
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}
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// This visitor seeds items that
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// 1) We want to explicitly consider as live:
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// * Item annotated with #[allow(dead_code)]
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// - This is done so that if we want to suppress warnings for a
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// group of dead functions, we only have to annotate the "root".
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// For example, if both `f` and `g` are dead and `f` calls `g`,
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// then annotating `f` with `#[allow(dead_code)]` will suppress
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// warning for both `f` and `g`.
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// * Item annotated with #[lang=".."]
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// - This is because lang items are always callable from elsewhere.
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// or
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// 2) We are not sure to be live or not
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// * Implementation of a trait method
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struct LifeSeeder<'k, 'tcx> {
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worklist: Vec<hir::HirId>,
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krate: &'k hir::Crate,
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tcx: TyCtxt<'tcx>,
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// see `MarkSymbolVisitor::struct_constructors`
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struct_constructors: FxHashMap<hir::HirId, hir::HirId>,
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}
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impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
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fn visit_item(&mut self, item: &hir::Item) {
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let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx,
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item.hir_id,
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&item.attrs);
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if allow_dead_code {
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self.worklist.push(item.hir_id);
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}
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match item.node {
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hir::ItemKind::Enum(ref enum_def, _) => {
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if allow_dead_code {
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self.worklist.extend(enum_def.variants.iter().map(|variant| variant.id));
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}
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for variant in &enum_def.variants {
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if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
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self.struct_constructors.insert(ctor_hir_id, variant.id);
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}
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}
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}
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hir::ItemKind::Trait(.., ref trait_item_refs) => {
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for trait_item_ref in trait_item_refs {
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let trait_item = self.krate.trait_item(trait_item_ref.id);
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match trait_item.node {
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hir::TraitItemKind::Const(_, Some(_)) |
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hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
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if has_allow_dead_code_or_lang_attr(self.tcx,
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trait_item.hir_id,
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&trait_item.attrs) {
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self.worklist.push(trait_item.hir_id);
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}
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}
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_ => {}
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}
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}
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}
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hir::ItemKind::Impl(.., ref opt_trait, _, ref impl_item_refs) => {
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for impl_item_ref in impl_item_refs {
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let impl_item = self.krate.impl_item(impl_item_ref.id);
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if opt_trait.is_some() ||
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has_allow_dead_code_or_lang_attr(self.tcx,
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impl_item.hir_id,
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&impl_item.attrs) {
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self.worklist.push(impl_item_ref.id.hir_id);
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}
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}
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}
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hir::ItemKind::Struct(ref variant_data, _) => {
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if let Some(ctor_hir_id) = variant_data.ctor_hir_id() {
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self.struct_constructors.insert(ctor_hir_id, item.hir_id);
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}
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}
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_ => ()
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}
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}
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fn visit_trait_item(&mut self, _item: &hir::TraitItem) {
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// ignore: we are handling this in `visit_item` above
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}
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fn visit_impl_item(&mut self, _item: &hir::ImplItem) {
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// ignore: we are handling this in `visit_item` above
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}
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}
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fn create_and_seed_worklist<'tcx>(
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tcx: TyCtxt<'tcx>,
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access_levels: &privacy::AccessLevels,
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krate: &hir::Crate,
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) -> (Vec<hir::HirId>, FxHashMap<hir::HirId, hir::HirId>) {
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let worklist = access_levels.map.iter().filter_map(|(&id, level)| {
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if level >= &privacy::AccessLevel::Reachable {
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Some(id)
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} else {
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None
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}
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}).chain(
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// Seed entry point
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tcx.entry_fn(LOCAL_CRATE).map(|(def_id, _)| tcx.hir().as_local_hir_id(def_id).unwrap())
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).collect::<Vec<_>>();
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// Seed implemented trait items
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let mut life_seeder = LifeSeeder {
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worklist,
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krate,
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tcx,
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struct_constructors: Default::default(),
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};
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krate.visit_all_item_likes(&mut life_seeder);
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(life_seeder.worklist, life_seeder.struct_constructors)
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}
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fn find_live<'tcx>(
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tcx: TyCtxt<'tcx>,
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access_levels: &privacy::AccessLevels,
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krate: &hir::Crate,
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) -> FxHashSet<hir::HirId> {
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let (worklist, struct_constructors) = create_and_seed_worklist(tcx, access_levels, krate);
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let mut symbol_visitor = MarkSymbolVisitor {
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worklist,
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tcx,
|
|
tables: &ty::TypeckTables::empty(None),
|
|
live_symbols: Default::default(),
|
|
repr_has_repr_c: false,
|
|
in_pat: false,
|
|
inherited_pub_visibility: false,
|
|
ignore_variant_stack: vec![],
|
|
struct_constructors,
|
|
};
|
|
symbol_visitor.mark_live_symbols();
|
|
symbol_visitor.live_symbols
|
|
}
|
|
|
|
struct DeadVisitor<'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
live_symbols: FxHashSet<hir::HirId>,
|
|
}
|
|
|
|
impl DeadVisitor<'tcx> {
|
|
fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
|
|
let should_warn = match item.node {
|
|
hir::ItemKind::Static(..)
|
|
| hir::ItemKind::Const(..)
|
|
| hir::ItemKind::Fn(..)
|
|
| hir::ItemKind::TyAlias(..)
|
|
| hir::ItemKind::Enum(..)
|
|
| hir::ItemKind::Struct(..)
|
|
| hir::ItemKind::Union(..) => true,
|
|
_ => false
|
|
};
|
|
should_warn && !self.symbol_is_live(item.hir_id)
|
|
}
|
|
|
|
fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
|
|
let field_type = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
|
|
!field.is_positional()
|
|
&& !self.symbol_is_live(field.hir_id)
|
|
&& !field_type.is_phantom_data()
|
|
&& !has_allow_dead_code_or_lang_attr(self.tcx, field.hir_id, &field.attrs)
|
|
}
|
|
|
|
fn should_warn_about_variant(&mut self, variant: &hir::Variant) -> bool {
|
|
!self.symbol_is_live(variant.id)
|
|
&& !has_allow_dead_code_or_lang_attr(self.tcx,
|
|
variant.id,
|
|
&variant.attrs)
|
|
}
|
|
|
|
fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem) -> bool {
|
|
!self.symbol_is_live(fi.hir_id)
|
|
&& !has_allow_dead_code_or_lang_attr(self.tcx, fi.hir_id, &fi.attrs)
|
|
}
|
|
|
|
// id := HIR id of an item's definition.
|
|
fn symbol_is_live(
|
|
&mut self,
|
|
id: hir::HirId,
|
|
) -> bool {
|
|
if self.live_symbols.contains(&id) {
|
|
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 def_id = self.tcx.hir().local_def_id(id);
|
|
let inherent_impls = self.tcx.inherent_impls(def_id);
|
|
for &impl_did in inherent_impls.iter() {
|
|
for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
|
|
if let Some(item_hir_id) = self.tcx.hir().as_local_hir_id(item_did) {
|
|
if self.live_symbols.contains(&item_hir_id) {
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
false
|
|
}
|
|
|
|
fn warn_dead_code(&mut self,
|
|
id: hir::HirId,
|
|
span: syntax_pos::Span,
|
|
name: ast::Name,
|
|
node_type: &str,
|
|
participle: &str) {
|
|
if !name.as_str().starts_with("_") {
|
|
self.tcx
|
|
.lint_hir(lint::builtin::DEAD_CODE,
|
|
id,
|
|
span,
|
|
&format!("{} is never {}: `{}`",
|
|
node_type, participle, name));
|
|
}
|
|
}
|
|
}
|
|
|
|
impl Visitor<'tcx> for DeadVisitor<'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 nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
|
|
NestedVisitorMap::All(&self.tcx.hir())
|
|
}
|
|
|
|
fn visit_item(&mut self, item: &'tcx hir::Item) {
|
|
if self.should_warn_about_item(item) {
|
|
// For items that have a definition with a signature followed by a
|
|
// block, point only at the signature.
|
|
let span = match item.node {
|
|
hir::ItemKind::Fn(..) |
|
|
hir::ItemKind::Mod(..) |
|
|
hir::ItemKind::Enum(..) |
|
|
hir::ItemKind::Struct(..) |
|
|
hir::ItemKind::Union(..) |
|
|
hir::ItemKind::Trait(..) |
|
|
hir::ItemKind::Impl(..) => self.tcx.sess.source_map().def_span(item.span),
|
|
_ => item.span,
|
|
};
|
|
let participle = match item.node {
|
|
hir::ItemKind::Struct(..) => "constructed", // Issue #52325
|
|
_ => "used"
|
|
};
|
|
self.warn_dead_code(
|
|
item.hir_id,
|
|
span,
|
|
item.ident.name,
|
|
item.node.descriptive_variant(),
|
|
participle,
|
|
);
|
|
} else {
|
|
// Only continue if we didn't warn
|
|
intravisit::walk_item(self, item);
|
|
}
|
|
}
|
|
|
|
fn visit_variant(&mut self,
|
|
variant: &'tcx hir::Variant,
|
|
g: &'tcx hir::Generics,
|
|
id: hir::HirId) {
|
|
if self.should_warn_about_variant(&variant) {
|
|
self.warn_dead_code(variant.id, variant.span, variant.ident.name,
|
|
"variant", "constructed");
|
|
} else {
|
|
intravisit::walk_variant(self, variant, g, id);
|
|
}
|
|
}
|
|
|
|
fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem) {
|
|
if self.should_warn_about_foreign_item(fi) {
|
|
self.warn_dead_code(fi.hir_id, fi.span, fi.ident.name,
|
|
fi.node.descriptive_variant(), "used");
|
|
}
|
|
intravisit::walk_foreign_item(self, fi);
|
|
}
|
|
|
|
fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
|
|
if self.should_warn_about_field(&field) {
|
|
self.warn_dead_code(field.hir_id, field.span, field.ident.name, "field", "used");
|
|
}
|
|
intravisit::walk_struct_field(self, field);
|
|
}
|
|
|
|
fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
|
|
match impl_item.node {
|
|
hir::ImplItemKind::Const(_, body_id) => {
|
|
if !self.symbol_is_live(impl_item.hir_id) {
|
|
self.warn_dead_code(impl_item.hir_id,
|
|
impl_item.span,
|
|
impl_item.ident.name,
|
|
"associated const",
|
|
"used");
|
|
}
|
|
self.visit_nested_body(body_id)
|
|
}
|
|
hir::ImplItemKind::Method(_, body_id) => {
|
|
if !self.symbol_is_live(impl_item.hir_id) {
|
|
let span = self.tcx.sess.source_map().def_span(impl_item.span);
|
|
self.warn_dead_code(impl_item.hir_id, span, impl_item.ident.name, "method",
|
|
"used");
|
|
}
|
|
self.visit_nested_body(body_id)
|
|
}
|
|
hir::ImplItemKind::OpaqueTy(..) |
|
|
hir::ImplItemKind::TyAlias(..) => {}
|
|
}
|
|
}
|
|
|
|
// Overwrite so that we don't warn the trait item itself.
|
|
fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
|
|
match trait_item.node {
|
|
hir::TraitItemKind::Const(_, Some(body_id)) |
|
|
hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
|
|
self.visit_nested_body(body_id)
|
|
}
|
|
hir::TraitItemKind::Const(_, None) |
|
|
hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) |
|
|
hir::TraitItemKind::Type(..) => {}
|
|
}
|
|
}
|
|
}
|
|
|
|
pub fn check_crate(tcx: TyCtxt<'_>) {
|
|
let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
|
|
let krate = tcx.hir().krate();
|
|
let live_symbols = find_live(tcx, access_levels, krate);
|
|
let mut visitor = DeadVisitor {
|
|
tcx,
|
|
live_symbols,
|
|
};
|
|
intravisit::walk_crate(&mut visitor, krate);
|
|
}
|