| // 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 rustc_data_structures::fx::{FxHashMap, FxHashSet}; |
| use rustc_hir as hir; |
| use rustc_hir::def::{CtorOf, DefKind, Res}; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor}; |
| use rustc_hir::itemlikevisit::ItemLikeVisitor; |
| use rustc_hir::{Node, PatKind, TyKind}; |
| use rustc_middle::hir::map::Map; |
| use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags; |
| use rustc_middle::middle::privacy; |
| use rustc_middle::ty::{self, DefIdTree, TyCtxt}; |
| use rustc_session::lint; |
| |
| use rustc_span::symbol::{sym, Symbol}; |
| |
| // Any local node that may call something in its body block should be |
| // explored. For example, if it's a live Node::Item 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(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool { |
| matches!( |
| tcx.hir().find(hir_id), |
| Some( |
| Node::Item(..) |
| | Node::ImplItem(..) |
| | Node::ForeignItem(..) |
| | Node::TraitItem(..) |
| | Node::Variant(..) |
| | Node::AnonConst(..) |
| | Node::Pat(..), |
| ) |
| ) |
| } |
| |
| struct MarkSymbolVisitor<'tcx> { |
| worklist: Vec<hir::HirId>, |
| tcx: TyCtxt<'tcx>, |
| maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>, |
| live_symbols: FxHashSet<hir::HirId>, |
| repr_has_repr_c: bool, |
| in_pat: bool, |
| inherited_pub_visibility: bool, |
| pub_visibility: bool, |
| ignore_variant_stack: Vec<DefId>, |
| // maps from tuple struct constructors to tuple struct items |
| struct_constructors: FxHashMap<hir::HirId, hir::HirId>, |
| } |
| |
| impl<'tcx> MarkSymbolVisitor<'tcx> { |
| /// Gets the type-checking results for the current body. |
| /// As this will ICE if called outside bodies, only call when working with |
| /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies). |
| #[track_caller] |
| fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> { |
| self.maybe_typeck_results |
| .expect("`MarkSymbolVisitor::typeck_results` called outside of body") |
| } |
| |
| fn check_def_id(&mut self, def_id: DefId) { |
| if let Some(def_id) = def_id.as_local() { |
| let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id); |
| if should_explore(self.tcx, hir_id) || self.struct_constructors.contains_key(&hir_id) { |
| self.worklist.push(hir_id); |
| } |
| self.live_symbols.insert(hir_id); |
| } |
| } |
| |
| fn insert_def_id(&mut self, def_id: DefId) { |
| if let Some(def_id) = def_id.as_local() { |
| let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id); |
| debug_assert!(!should_explore(self.tcx, hir_id)); |
| self.live_symbols.insert(hir_id); |
| } |
| } |
| |
| fn handle_res(&mut self, res: Res) { |
| match res { |
| Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::TyAlias, _) => { |
| self.check_def_id(res.def_id()); |
| } |
| _ if self.in_pat => {} |
| Res::PrimTy(..) | Res::SelfCtor(..) | Res::Local(..) => {} |
| Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => { |
| let variant_id = self.tcx.parent(ctor_def_id).unwrap(); |
| let enum_id = self.tcx.parent(variant_id).unwrap(); |
| self.check_def_id(enum_id); |
| if !self.ignore_variant_stack.contains(&ctor_def_id) { |
| self.check_def_id(variant_id); |
| } |
| } |
| Res::Def(DefKind::Variant, variant_id) => { |
| let enum_id = self.tcx.parent(variant_id).unwrap(); |
| self.check_def_id(enum_id); |
| if !self.ignore_variant_stack.contains(&variant_id) { |
| self.check_def_id(variant_id); |
| } |
| } |
| Res::SelfTy(t, i) => { |
| if let Some(t) = t { |
| self.check_def_id(t); |
| } |
| if let Some((i, _)) = i { |
| self.check_def_id(i); |
| } |
| } |
| Res::ToolMod | Res::NonMacroAttr(..) | Res::Err => {} |
| _ => { |
| self.check_def_id(res.def_id()); |
| } |
| } |
| } |
| |
| fn lookup_and_handle_method(&mut self, id: hir::HirId) { |
| if let Some(def_id) = self.typeck_results().type_dependent_def_id(id) { |
| self.check_def_id(def_id); |
| } else { |
| bug!("no type-dependent def for method"); |
| } |
| } |
| |
| fn handle_field_access(&mut self, lhs: &hir::Expr<'_>, hir_id: hir::HirId) { |
| match self.typeck_results().expr_ty_adjusted(lhs).kind() { |
| ty::Adt(def, _) => { |
| let index = self.tcx.field_index(hir_id, self.typeck_results()); |
| self.insert_def_id(def.non_enum_variant().fields[index].did); |
| } |
| ty::Tuple(..) => {} |
| _ => span_bug!(lhs.span, "named field access on non-ADT"), |
| } |
| } |
| |
| #[allow(dead_code)] // FIXME(81658): should be used + lint reinstated after #83171 relands. |
| fn handle_assign(&mut self, expr: &'tcx hir::Expr<'tcx>) { |
| if self |
| .typeck_results() |
| .expr_adjustments(expr) |
| .iter() |
| .any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(_))) |
| { |
| self.visit_expr(expr); |
| } else if let hir::ExprKind::Field(base, ..) = expr.kind { |
| // Ignore write to field |
| self.handle_assign(base); |
| } else { |
| self.visit_expr(expr); |
| } |
| } |
| |
| #[allow(dead_code)] // FIXME(81658): should be used + lint reinstated after #83171 relands. |
| fn check_for_self_assign(&mut self, assign: &'tcx hir::Expr<'tcx>) { |
| fn check_for_self_assign_helper( |
| tcx: TyCtxt<'tcx>, |
| typeck_results: &'tcx ty::TypeckResults<'tcx>, |
| lhs: &'tcx hir::Expr<'tcx>, |
| rhs: &'tcx hir::Expr<'tcx>, |
| ) -> bool { |
| match (&lhs.kind, &rhs.kind) { |
| (hir::ExprKind::Path(ref qpath_l), hir::ExprKind::Path(ref qpath_r)) => { |
| if let (Res::Local(id_l), Res::Local(id_r)) = ( |
| typeck_results.qpath_res(qpath_l, lhs.hir_id), |
| typeck_results.qpath_res(qpath_r, rhs.hir_id), |
| ) { |
| if id_l == id_r { |
| return true; |
| } |
| } |
| return false; |
| } |
| (hir::ExprKind::Field(lhs_l, ident_l), hir::ExprKind::Field(lhs_r, ident_r)) => { |
| if ident_l == ident_r { |
| return check_for_self_assign_helper(tcx, typeck_results, lhs_l, lhs_r); |
| } |
| return false; |
| } |
| _ => { |
| return false; |
| } |
| } |
| } |
| |
| if let hir::ExprKind::Assign(lhs, rhs, _) = assign.kind { |
| if check_for_self_assign_helper(self.tcx, self.typeck_results(), lhs, rhs) |
| && !assign.span.from_expansion() |
| { |
| let is_field_assign = matches!(lhs.kind, hir::ExprKind::Field(..)); |
| self.tcx.struct_span_lint_hir( |
| lint::builtin::DEAD_CODE, |
| assign.hir_id, |
| assign.span, |
| |lint| { |
| lint.build(&format!( |
| "useless assignment of {} of type `{}` to itself", |
| if is_field_assign { "field" } else { "variable" }, |
| self.typeck_results().expr_ty(lhs), |
| )) |
| .emit(); |
| }, |
| ) |
| } |
| } |
| } |
| |
| fn handle_field_pattern_match( |
| &mut self, |
| lhs: &hir::Pat<'_>, |
| res: Res, |
| pats: &[hir::PatField<'_>], |
| ) { |
| let variant = match self.typeck_results().node_type(lhs.hir_id).kind() { |
| ty::Adt(adt, _) => adt.variant_of_res(res), |
| _ => span_bug!(lhs.span, "non-ADT in struct pattern"), |
| }; |
| for pat in pats { |
| if let PatKind::Wild = pat.pat.kind { |
| continue; |
| } |
| let index = self.tcx.field_index(pat.hir_id, self.typeck_results()); |
| self.insert_def_id(variant.fields[index].did); |
| } |
| } |
| |
| fn mark_live_symbols(&mut self) { |
| let mut scanned = FxHashSet::default(); |
| while let Some(id) = self.worklist.pop() { |
| if !scanned.insert(id) { |
| continue; |
| } |
| |
| // in the case of tuple struct constructors we want to check the item, not the generated |
| // tuple struct constructor function |
| let id = self.struct_constructors.get(&id).cloned().unwrap_or(id); |
| |
| if let Some(node) = self.tcx.hir().find(id) { |
| self.live_symbols.insert(id); |
| self.visit_node(node); |
| } |
| } |
| } |
| |
| fn visit_node(&mut self, node: Node<'tcx>) { |
| let had_repr_c = self.repr_has_repr_c; |
| let had_inherited_pub_visibility = self.inherited_pub_visibility; |
| let had_pub_visibility = self.pub_visibility; |
| self.repr_has_repr_c = false; |
| self.inherited_pub_visibility = false; |
| self.pub_visibility = false; |
| match node { |
| Node::Item(item) => { |
| self.pub_visibility = item.vis.node.is_pub(); |
| |
| match item.kind { |
| hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => { |
| let def = self.tcx.adt_def(item.def_id); |
| self.repr_has_repr_c = def.repr.c(); |
| |
| intravisit::walk_item(self, &item); |
| } |
| hir::ItemKind::Enum(..) => { |
| self.inherited_pub_visibility = self.pub_visibility; |
| |
| intravisit::walk_item(self, &item); |
| } |
| hir::ItemKind::ForeignMod { .. } => {} |
| _ => { |
| intravisit::walk_item(self, &item); |
| } |
| } |
| } |
| Node::TraitItem(trait_item) => { |
| intravisit::walk_trait_item(self, trait_item); |
| } |
| Node::ImplItem(impl_item) => { |
| intravisit::walk_impl_item(self, impl_item); |
| } |
| Node::ForeignItem(foreign_item) => { |
| intravisit::walk_foreign_item(self, &foreign_item); |
| } |
| _ => {} |
| } |
| self.pub_visibility = had_pub_visibility; |
| self.inherited_pub_visibility = had_inherited_pub_visibility; |
| self.repr_has_repr_c = had_repr_c; |
| } |
| |
| fn mark_as_used_if_union(&mut self, adt: &ty::AdtDef, fields: &[hir::ExprField<'_>]) { |
| if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did.is_local() { |
| for field in fields { |
| let index = self.tcx.field_index(field.hir_id, self.typeck_results()); |
| self.insert_def_id(adt.non_enum_variant().fields[index].did); |
| } |
| } |
| } |
| } |
| |
| impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> { |
| type Map = intravisit::ErasedMap<'tcx>; |
| |
| fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> { |
| NestedVisitorMap::None |
| } |
| |
| fn visit_nested_body(&mut self, body: hir::BodyId) { |
| let old_maybe_typeck_results = |
| self.maybe_typeck_results.replace(self.tcx.typeck_body(body)); |
| let body = self.tcx.hir().body(body); |
| self.visit_body(body); |
| self.maybe_typeck_results = old_maybe_typeck_results; |
| } |
| |
| fn visit_variant_data( |
| &mut self, |
| def: &'tcx hir::VariantData<'tcx>, |
| _: Symbol, |
| _: &hir::Generics<'_>, |
| _: hir::HirId, |
| _: rustc_span::Span, |
| ) { |
| let has_repr_c = self.repr_has_repr_c; |
| let inherited_pub_visibility = self.inherited_pub_visibility; |
| let pub_visibility = self.pub_visibility; |
| let live_fields = def.fields().iter().filter(|f| { |
| has_repr_c || (pub_visibility && (inherited_pub_visibility || f.vis.node.is_pub())) |
| }); |
| self.live_symbols.extend(live_fields.map(|f| f.hir_id)); |
| |
| intravisit::walk_struct_def(self, def); |
| } |
| |
| fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) { |
| match expr.kind { |
| hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => { |
| let res = self.typeck_results().qpath_res(qpath, expr.hir_id); |
| self.handle_res(res); |
| } |
| hir::ExprKind::MethodCall(..) => { |
| self.lookup_and_handle_method(expr.hir_id); |
| } |
| hir::ExprKind::Field(ref lhs, ..) => { |
| self.handle_field_access(&lhs, expr.hir_id); |
| } |
| hir::ExprKind::Struct(ref qpath, ref fields, _) => { |
| let res = self.typeck_results().qpath_res(qpath, expr.hir_id); |
| self.handle_res(res); |
| if let ty::Adt(ref adt, _) = self.typeck_results().expr_ty(expr).kind() { |
| self.mark_as_used_if_union(adt, fields); |
| } |
| } |
| _ => (), |
| } |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) { |
| // 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(arm.pat.necessary_variants()); |
| intravisit::walk_arm(self, arm); |
| self.ignore_variant_stack.truncate(len); |
| } |
| |
| fn visit_pat(&mut self, pat: &'tcx hir::Pat<'tcx>) { |
| self.in_pat = true; |
| match pat.kind { |
| PatKind::Struct(ref path, ref fields, _) => { |
| let res = self.typeck_results().qpath_res(path, pat.hir_id); |
| self.handle_field_pattern_match(pat, res, fields); |
| } |
| PatKind::Path(ref qpath) => { |
| let res = self.typeck_results().qpath_res(qpath, pat.hir_id); |
| self.handle_res(res); |
| } |
| _ => (), |
| } |
| |
| intravisit::walk_pat(self, pat); |
| self.in_pat = false; |
| } |
| |
| fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) { |
| self.handle_res(path.res); |
| intravisit::walk_path(self, path); |
| } |
| |
| fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) { |
| if let TyKind::OpaqueDef(item_id, _) = ty.kind { |
| let item = self.tcx.hir().item(item_id); |
| intravisit::walk_item(self, item); |
| } |
| intravisit::walk_ty(self, ty); |
| } |
| |
| fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) { |
| self.live_symbols.insert(c.hir_id); |
| intravisit::walk_anon_const(self, c); |
| } |
| } |
| |
| fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, id: hir::HirId) -> bool { |
| let attrs = tcx.hir().attrs(id); |
| if tcx.sess.contains_name(attrs, sym::lang) { |
| return true; |
| } |
| |
| // Stable attribute for #[lang = "panic_impl"] |
| if tcx.sess.contains_name(attrs, sym::panic_handler) { |
| return true; |
| } |
| |
| // (To be) stable attribute for #[lang = "oom"] |
| if tcx.sess.contains_name(attrs, sym::alloc_error_handler) { |
| return true; |
| } |
| |
| let def_id = tcx.hir().local_def_id(id); |
| let cg_attrs = tcx.codegen_fn_attrs(def_id); |
| |
| // #[used], #[no_mangle], #[export_name], etc also keeps the item alive |
| // forcefully, e.g., for placing it in a specific section. |
| if cg_attrs.contains_extern_indicator() || cg_attrs.flags.contains(CodegenFnAttrFlags::USED) { |
| return true; |
| } |
| |
| tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow |
| } |
| |
| // 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 |
| // * Implementations of traits and trait methods |
| struct LifeSeeder<'k, 'tcx> { |
| worklist: Vec<hir::HirId>, |
| krate: &'k hir::Crate<'k>, |
| tcx: TyCtxt<'tcx>, |
| // see `MarkSymbolVisitor::struct_constructors` |
| struct_constructors: FxHashMap<hir::HirId, hir::HirId>, |
| } |
| |
| impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> { |
| fn visit_item(&mut self, item: &hir::Item<'_>) { |
| let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx, item.hir_id()); |
| if allow_dead_code { |
| self.worklist.push(item.hir_id()); |
| } |
| match item.kind { |
| hir::ItemKind::Enum(ref enum_def, _) => { |
| if allow_dead_code { |
| self.worklist.extend(enum_def.variants.iter().map(|variant| variant.id)); |
| } |
| |
| for variant in enum_def.variants { |
| if let Some(ctor_hir_id) = variant.data.ctor_hir_id() { |
| self.struct_constructors.insert(ctor_hir_id, variant.id); |
| } |
| } |
| } |
| hir::ItemKind::Impl(hir::Impl { ref of_trait, items, .. }) => { |
| if of_trait.is_some() { |
| self.worklist.push(item.hir_id()); |
| } |
| for impl_item_ref in items { |
| let impl_item = self.krate.impl_item(impl_item_ref.id); |
| if of_trait.is_some() |
| || has_allow_dead_code_or_lang_attr(self.tcx, impl_item.hir_id()) |
| { |
| self.worklist.push(impl_item_ref.id.hir_id()); |
| } |
| } |
| } |
| hir::ItemKind::Struct(ref variant_data, _) => { |
| if let Some(ctor_hir_id) = variant_data.ctor_hir_id() { |
| self.struct_constructors.insert(ctor_hir_id, item.hir_id()); |
| } |
| } |
| _ => (), |
| } |
| } |
| |
| fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) { |
| use hir::TraitItemKind::{Const, Fn}; |
| if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_))) |
| && has_allow_dead_code_or_lang_attr(self.tcx, trait_item.hir_id()) |
| { |
| self.worklist.push(trait_item.hir_id()); |
| } |
| } |
| |
| fn visit_impl_item(&mut self, _item: &hir::ImplItem<'_>) { |
| // ignore: we are handling this in `visit_item` above |
| } |
| |
| fn visit_foreign_item(&mut self, foreign_item: &hir::ForeignItem<'_>) { |
| use hir::ForeignItemKind::{Fn, Static}; |
| if matches!(foreign_item.kind, Static(..) | Fn(..)) |
| && has_allow_dead_code_or_lang_attr(self.tcx, foreign_item.hir_id()) |
| { |
| self.worklist.push(foreign_item.hir_id()); |
| } |
| } |
| } |
| |
| fn create_and_seed_worklist<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| access_levels: &privacy::AccessLevels, |
| krate: &hir::Crate<'_>, |
| ) -> (Vec<hir::HirId>, FxHashMap<hir::HirId, hir::HirId>) { |
| let worklist = access_levels |
| .map |
| .iter() |
| .filter_map( |
| |(&id, &level)| { |
| if level >= privacy::AccessLevel::Reachable { Some(id) } else { None } |
| }, |
| ) |
| .chain( |
| // Seed entry point |
| tcx.entry_fn(()).and_then(|(def_id, _)| { |
| def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id)) |
| }), |
| ) |
| .collect::<Vec<_>>(); |
| |
| // Seed implemented trait items |
| let mut life_seeder = |
| LifeSeeder { worklist, krate, tcx, struct_constructors: Default::default() }; |
| krate.visit_all_item_likes(&mut life_seeder); |
| |
| (life_seeder.worklist, life_seeder.struct_constructors) |
| } |
| |
| fn find_live<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| access_levels: &privacy::AccessLevels, |
| krate: &hir::Crate<'_>, |
| ) -> FxHashSet<hir::HirId> { |
| let (worklist, struct_constructors) = create_and_seed_worklist(tcx, access_levels, krate); |
| let mut symbol_visitor = MarkSymbolVisitor { |
| worklist, |
| tcx, |
| maybe_typeck_results: None, |
| live_symbols: Default::default(), |
| repr_has_repr_c: false, |
| in_pat: false, |
| inherited_pub_visibility: false, |
| 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 = matches!( |
| item.kind, |
| hir::ItemKind::Static(..) |
| | hir::ItemKind::Const(..) |
| | hir::ItemKind::Fn(..) |
| | hir::ItemKind::TyAlias(..) |
| | hir::ItemKind::Enum(..) |
| | hir::ItemKind::Struct(..) |
| | hir::ItemKind::Union(..) |
| ); |
| should_warn && !self.symbol_is_live(item.hir_id()) |
| } |
| |
| fn should_warn_about_field(&mut self, field: &hir::FieldDef<'_>) -> 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) |
| } |
| |
| 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) |
| } |
| |
| 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()) |
| } |
| |
| // 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(did) = item_did.as_local() { |
| let item_hir_id = self.tcx.hir().local_def_id_to_hir_id(did); |
| if self.live_symbols.contains(&item_hir_id) { |
| return true; |
| } |
| } |
| } |
| } |
| false |
| } |
| |
| fn warn_dead_code( |
| &mut self, |
| id: hir::HirId, |
| span: rustc_span::Span, |
| name: Symbol, |
| participle: &str, |
| ) { |
| if !name.as_str().starts_with('_') { |
| self.tcx.struct_span_lint_hir(lint::builtin::DEAD_CODE, id, span, |lint| { |
| let def_id = self.tcx.hir().local_def_id(id); |
| let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id()); |
| lint.build(&format!("{} is never {}: `{}`", descr, participle, name)).emit() |
| }); |
| } |
| } |
| } |
| |
| impl Visitor<'tcx> for DeadVisitor<'tcx> { |
| type Map = Map<'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(&mut self) -> NestedVisitorMap<Self::Map> { |
| NestedVisitorMap::All(self.tcx.hir()) |
| } |
| |
| fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) { |
| if self.should_warn_about_item(item) { |
| // For most items, we want to highlight its identifier |
| let span = match item.kind { |
| hir::ItemKind::Fn(..) |
| | hir::ItemKind::Mod(..) |
| | hir::ItemKind::Enum(..) |
| | hir::ItemKind::Struct(..) |
| | hir::ItemKind::Union(..) |
| | hir::ItemKind::Trait(..) |
| | hir::ItemKind::Impl { .. } => { |
| // FIXME(66095): Because item.span is annotated with things |
| // like expansion data, and ident.span isn't, we use the |
| // def_span method if it's part of a macro invocation |
| // (and thus has a source_callee set). |
| // We should probably annotate ident.span with the macro |
| // context, but that's a larger change. |
| if item.span.source_callee().is_some() { |
| self.tcx.sess.source_map().guess_head_span(item.span) |
| } else { |
| item.ident.span |
| } |
| } |
| _ => item.span, |
| }; |
| let participle = match item.kind { |
| hir::ItemKind::Struct(..) => "constructed", // Issue #52325 |
| _ => "used", |
| }; |
| self.warn_dead_code(item.hir_id(), span, item.ident.name, participle); |
| } else { |
| // Only continue if we didn't warn |
| intravisit::walk_item(self, item); |
| } |
| } |
| |
| fn visit_variant( |
| &mut self, |
| variant: &'tcx hir::Variant<'tcx>, |
| g: &'tcx hir::Generics<'tcx>, |
| id: hir::HirId, |
| ) { |
| if self.should_warn_about_variant(&variant) { |
| self.warn_dead_code(variant.id, variant.span, variant.ident.name, "constructed"); |
| } else { |
| intravisit::walk_variant(self, variant, g, id); |
| } |
| } |
| |
| fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem<'tcx>) { |
| if self.should_warn_about_foreign_item(fi) { |
| self.warn_dead_code(fi.hir_id(), fi.span, fi.ident.name, "used"); |
| } |
| intravisit::walk_foreign_item(self, fi); |
| } |
| |
| fn visit_field_def(&mut self, field: &'tcx hir::FieldDef<'tcx>) { |
| if self.should_warn_about_field(&field) { |
| self.warn_dead_code(field.hir_id, field.span, field.ident.name, "read"); |
| } |
| intravisit::walk_field_def(self, field); |
| } |
| |
| fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) { |
| match impl_item.kind { |
| 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, |
| "used", |
| ); |
| } |
| self.visit_nested_body(body_id) |
| } |
| hir::ImplItemKind::Fn(_, body_id) => { |
| if !self.symbol_is_live(impl_item.hir_id()) { |
| // FIXME(66095): Because impl_item.span is annotated with things |
| // like expansion data, and ident.span isn't, we use the |
| // def_span method if it's part of a macro invocation |
| // (and thus has a source_callee set). |
| // We should probably annotate ident.span with the macro |
| // context, but that's a larger change. |
| let span = if impl_item.span.source_callee().is_some() { |
| self.tcx.sess.source_map().guess_head_span(impl_item.span) |
| } else { |
| impl_item.ident.span |
| }; |
| self.warn_dead_code(impl_item.hir_id(), span, impl_item.ident.name, "used"); |
| } |
| self.visit_nested_body(body_id) |
| } |
| 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<'tcx>) { |
| match trait_item.kind { |
| hir::TraitItemKind::Const(_, Some(body_id)) |
| | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => { |
| self.visit_nested_body(body_id) |
| } |
| hir::TraitItemKind::Const(_, None) |
| | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) |
| | hir::TraitItemKind::Type(..) => {} |
| } |
| } |
| } |
| |
| pub fn check_crate(tcx: TyCtxt<'_>) { |
| let access_levels = &tcx.privacy_access_levels(()); |
| 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); |
| } |
