| // This implements the dead-code warning pass. |
| // All reachable symbols are live, code called from live code is live, code with certain lint |
| // expectations such as `#[expect(unused)]` and `#[expect(dead_code)]` is live, and everything else |
| // is dead. |
| |
| use hir::def_id::{LocalDefIdMap, LocalDefIdSet}; |
| use itertools::Itertools; |
| use rustc_data_structures::unord::UnordSet; |
| use rustc_errors::MultiSpan; |
| use rustc_hir as hir; |
| use rustc_hir::def::{CtorOf, DefKind, Res}; |
| use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId}; |
| use rustc_hir::intravisit::{self, Visitor}; |
| use rustc_hir::{Node, PatKind, TyKind}; |
| use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags; |
| use rustc_middle::middle::privacy::Level; |
| use rustc_middle::query::Providers; |
| use rustc_middle::ty::{self, TyCtxt}; |
| use rustc_session::lint; |
| use rustc_span::symbol::{sym, Symbol}; |
| use rustc_target::abi::FieldIdx; |
| use std::mem; |
| |
| use crate::errors::{ |
| ChangeFieldsToBeOfUnitType, IgnoredDerivedImpls, MultipleDeadCodes, ParentInfo, |
| UselessAssignment, |
| }; |
| |
| // 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<'_>, def_id: LocalDefId) -> bool { |
| matches!( |
| tcx.hir().find_by_def_id(def_id), |
| Some( |
| Node::Item(..) |
| | Node::ImplItem(..) |
| | Node::ForeignItem(..) |
| | Node::TraitItem(..) |
| | Node::Variant(..) |
| | Node::AnonConst(..) |
| ) |
| ) |
| } |
| |
| /// Determine if a work from the worklist is coming from the a `#[allow]` |
| /// or a `#[expect]` of `dead_code` |
| #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)] |
| enum ComesFromAllowExpect { |
| Yes, |
| No, |
| } |
| |
| struct MarkSymbolVisitor<'tcx> { |
| worklist: Vec<(LocalDefId, ComesFromAllowExpect)>, |
| tcx: TyCtxt<'tcx>, |
| maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>, |
| live_symbols: LocalDefIdSet, |
| repr_has_repr_c: bool, |
| repr_has_repr_simd: bool, |
| in_pat: bool, |
| ignore_variant_stack: Vec<DefId>, |
| // maps from tuple struct constructors to tuple struct items |
| struct_constructors: LocalDefIdMap<LocalDefId>, |
| // maps from ADTs to ignored derived traits (e.g. Debug and Clone) |
| // and the span of their respective impl (i.e., part of the derive |
| // macro) |
| ignored_derived_traits: LocalDefIdMap<Vec<(DefId, DefId)>>, |
| } |
| |
| 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() { |
| if should_explore(self.tcx, def_id) || self.struct_constructors.contains_key(&def_id) { |
| self.worklist.push((def_id, ComesFromAllowExpect::No)); |
| } |
| self.live_symbols.insert(def_id); |
| } |
| } |
| |
| fn insert_def_id(&mut self, def_id: DefId) { |
| if let Some(def_id) = def_id.as_local() { |
| debug_assert!(!should_explore(self.tcx, def_id)); |
| self.live_symbols.insert(def_id); |
| } |
| } |
| |
| fn handle_res(&mut self, res: Res) { |
| match res { |
| Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::TyAlias, def_id) => { |
| self.check_def_id(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); |
| let enum_id = self.tcx.parent(variant_id); |
| 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); |
| self.check_def_id(enum_id); |
| if !self.ignore_variant_stack.contains(&variant_id) { |
| self.check_def_id(variant_id); |
| } |
| } |
| Res::Def(_, def_id) => self.check_def_id(def_id), |
| Res::SelfTyParam { trait_: t } => self.check_def_id(t), |
| Res::SelfTyAlias { alias_to: i, .. } => self.check_def_id(i), |
| Res::ToolMod | Res::NonMacroAttr(..) | Res::Err => {} |
| } |
| } |
| |
| 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.typeck_results().field_index(hir_id); |
| 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>( |
| 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(typeck_results, lhs_l, lhs_r); |
| } |
| return false; |
| } |
| _ => { |
| return false; |
| } |
| } |
| } |
| |
| if let hir::ExprKind::Assign(lhs, rhs, _) = assign.kind |
| && check_for_self_assign_helper(self.typeck_results(), lhs, rhs) |
| && !assign.span.from_expansion() |
| { |
| let is_field_assign = matches!(lhs.kind, hir::ExprKind::Field(..)); |
| self.tcx.emit_spanned_lint( |
| lint::builtin::DEAD_CODE, |
| assign.hir_id, |
| assign.span, |
| UselessAssignment { is_field_assign, ty: self.typeck_results().expr_ty(lhs) }, |
| ) |
| } |
| } |
| |
| 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.typeck_results().field_index(pat.hir_id); |
| self.insert_def_id(variant.fields[index].did); |
| } |
| } |
| |
| fn handle_tuple_field_pattern_match( |
| &mut self, |
| lhs: &hir::Pat<'_>, |
| res: Res, |
| pats: &[hir::Pat<'_>], |
| dotdot: hir::DotDotPos, |
| ) { |
| 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 tuple struct pattern"), |
| }; |
| let dotdot = dotdot.as_opt_usize().unwrap_or(pats.len()); |
| let first_n = pats.iter().enumerate().take(dotdot); |
| let missing = variant.fields.len() - pats.len(); |
| let last_n = pats.iter().enumerate().skip(dotdot).map(|(idx, pat)| (idx + missing, pat)); |
| for (idx, pat) in first_n.chain(last_n) { |
| if let PatKind::Wild = pat.kind { |
| continue; |
| } |
| self.insert_def_id(variant.fields[FieldIdx::from_usize(idx)].did); |
| } |
| } |
| |
| fn handle_offset_of(&mut self, expr: &'tcx hir::Expr<'tcx>) { |
| let data = self.typeck_results().offset_of_data(); |
| let &(container, ref indices) = |
| data.get(expr.hir_id).expect("no offset_of_data for offset_of"); |
| |
| let body_did = self.typeck_results().hir_owner.to_def_id(); |
| let param_env = self.tcx.param_env(body_did); |
| |
| let mut current_ty = container; |
| |
| for &(variant, field) in indices { |
| match current_ty.kind() { |
| ty::Adt(def, subst) => { |
| let field = &def.variant(variant).fields[field]; |
| |
| self.insert_def_id(field.did); |
| let field_ty = field.ty(self.tcx, subst); |
| |
| current_ty = self.tcx.normalize_erasing_regions(param_env, field_ty); |
| } |
| // we don't need to mark tuple fields as live, |
| // but we may need to mark subfields |
| ty::Tuple(tys) => { |
| current_ty = |
| self.tcx.normalize_erasing_regions(param_env, tys[field.as_usize()]); |
| } |
| _ => span_bug!(expr.span, "named field access on non-ADT"), |
| } |
| } |
| } |
| |
| fn mark_live_symbols(&mut self) { |
| let mut scanned = UnordSet::default(); |
| while let Some(work) = self.worklist.pop() { |
| if !scanned.insert(work) { |
| continue; |
| } |
| |
| let (id, comes_from_allow_expect) = work; |
| |
| // Avoid accessing the HIR for the synthesized associated type generated for RPITITs. |
| if self.tcx.is_impl_trait_in_trait(id.to_def_id()) { |
| self.live_symbols.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).copied().unwrap_or(id); |
| |
| if let Some(node) = self.tcx.hir().find_by_def_id(id) { |
| // When using `#[allow]` or `#[expect]` of `dead_code`, we do a QOL improvement |
| // by declaring fn calls, statics, ... within said items as live, as well as |
| // the item itself, although technically this is not the case. |
| // |
| // This means that the lint for said items will never be fired. |
| // |
| // This doesn't make any difference for the item declared with `#[allow]`, as |
| // the lint firing will be a nop, as it will be silenced by the `#[allow]` of |
| // the item. |
| // |
| // However, for `#[expect]`, the presence or absence of the lint is relevant, |
| // so we don't add it to the list of live symbols when it comes from a |
| // `#[expect]`. This means that we will correctly report an item as live or not |
| // for the `#[expect]` case. |
| // |
| // Note that an item can and will be duplicated on the worklist with different |
| // `ComesFromAllowExpect`, particulary if it was added from the |
| // `effective_visibilities` query or from the `#[allow]`/`#[expect]` checks, |
| // this "duplication" is essential as otherwise a function with `#[expect]` |
| // called from a `pub fn` may be falsely reported as not live, falsely |
| // triggering the `unfulfilled_lint_expectations` lint. |
| if comes_from_allow_expect != ComesFromAllowExpect::Yes { |
| self.live_symbols.insert(id); |
| } |
| self.visit_node(node); |
| } |
| } |
| } |
| |
| /// Automatically generated items marked with `rustc_trivial_field_reads` |
| /// will be ignored for the purposes of dead code analysis (see PR #85200 |
| /// for discussion). |
| fn should_ignore_item(&mut self, def_id: DefId) -> bool { |
| if let Some(impl_of) = self.tcx.impl_of_method(def_id) { |
| if !self.tcx.is_automatically_derived(impl_of) { |
| return false; |
| } |
| |
| if let Some(trait_of) = self.tcx.trait_id_of_impl(impl_of) |
| && self.tcx.has_attr(trait_of, sym::rustc_trivial_field_reads) |
| { |
| let trait_ref = self.tcx.impl_trait_ref(impl_of).unwrap().instantiate_identity(); |
| if let ty::Adt(adt_def, _) = trait_ref.self_ty().kind() |
| && let Some(adt_def_id) = adt_def.did().as_local() |
| { |
| self.ignored_derived_traits |
| .entry(adt_def_id) |
| .or_default() |
| .push((trait_of, impl_of)); |
| } |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| fn visit_node(&mut self, node: Node<'tcx>) { |
| if let Node::ImplItem(hir::ImplItem { owner_id, .. }) = node |
| && self.should_ignore_item(owner_id.to_def_id()) |
| { |
| return; |
| } |
| |
| let had_repr_c = self.repr_has_repr_c; |
| let had_repr_simd = self.repr_has_repr_simd; |
| self.repr_has_repr_c = false; |
| self.repr_has_repr_simd = false; |
| match node { |
| Node::Item(item) => match item.kind { |
| hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => { |
| let def = self.tcx.adt_def(item.owner_id); |
| self.repr_has_repr_c = def.repr().c(); |
| self.repr_has_repr_simd = def.repr().simd(); |
| |
| 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) => { |
| let item = self.tcx.local_parent(impl_item.owner_id.def_id); |
| if self.tcx.impl_trait_ref(item).is_none() { |
| //// 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 self_ty = self.tcx.type_of(item).instantiate_identity(); |
| match *self_ty.kind() { |
| ty::Adt(def, _) => self.check_def_id(def.did()), |
| ty::Foreign(did) => self.check_def_id(did), |
| ty::Dynamic(data, ..) => { |
| if let Some(def_id) = data.principal_def_id() { |
| self.check_def_id(def_id) |
| } |
| } |
| _ => {} |
| } |
| } |
| intravisit::walk_impl_item(self, impl_item); |
| } |
| Node::ForeignItem(foreign_item) => { |
| intravisit::walk_foreign_item(self, &foreign_item); |
| } |
| _ => {} |
| } |
| self.repr_has_repr_simd = had_repr_simd; |
| self.repr_has_repr_c = had_repr_c; |
| } |
| |
| fn mark_as_used_if_union(&mut self, adt: ty::AdtDef<'tcx>, 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.typeck_results().field_index(field.hir_id); |
| self.insert_def_id(adt.non_enum_variant().fields[index].did); |
| } |
| } |
| } |
| } |
| |
| impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> { |
| 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>) { |
| let tcx = self.tcx; |
| let has_repr_c = self.repr_has_repr_c; |
| let has_repr_simd = self.repr_has_repr_simd; |
| let live_fields = def.fields().iter().filter_map(|f| { |
| let def_id = f.def_id; |
| if has_repr_c || (f.is_positional() && has_repr_simd) { |
| return Some(def_id); |
| } |
| if !tcx.visibility(f.hir_id.owner.def_id).is_public() { |
| return None; |
| } |
| if tcx.visibility(def_id).is_public() { Some(def_id) } else { None } |
| }); |
| self.live_symbols.extend(live_fields); |
| |
| 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(adt, _) = self.typeck_results().expr_ty(expr).kind() { |
| self.mark_as_used_if_union(*adt, fields); |
| } |
| } |
| hir::ExprKind::Closure(cls) => { |
| self.insert_def_id(cls.def_id.to_def_id()); |
| } |
| hir::ExprKind::OffsetOf(..) => { |
| self.handle_offset_of(expr); |
| } |
| _ => (), |
| } |
| |
| 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); |
| } |
| PatKind::TupleStruct(ref qpath, ref fields, dotdot) => { |
| let res = self.typeck_results().qpath_res(qpath, pat.hir_id); |
| self.handle_tuple_field_pattern_match(pat, res, fields, dotdot); |
| } |
| _ => (), |
| } |
| |
| intravisit::walk_pat(self, pat); |
| self.in_pat = false; |
| } |
| |
| fn visit_path(&mut self, path: &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) { |
| // When inline const blocks are used in pattern position, paths |
| // referenced by it should be considered as used. |
| let in_pat = mem::replace(&mut self.in_pat, false); |
| |
| self.live_symbols.insert(c.def_id); |
| intravisit::walk_anon_const(self, c); |
| |
| self.in_pat = in_pat; |
| } |
| |
| fn visit_inline_const(&mut self, c: &'tcx hir::ConstBlock) { |
| // When inline const blocks are used in pattern position, paths |
| // referenced by it should be considered as used. |
| let in_pat = mem::replace(&mut self.in_pat, false); |
| |
| self.live_symbols.insert(c.def_id); |
| intravisit::walk_inline_const(self, c); |
| |
| self.in_pat = in_pat; |
| } |
| } |
| |
| fn has_allow_dead_code_or_lang_attr( |
| tcx: TyCtxt<'_>, |
| def_id: LocalDefId, |
| ) -> Option<ComesFromAllowExpect> { |
| fn has_lang_attr(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool { |
| tcx.has_attr(def_id, sym::lang) |
| // Stable attribute for #[lang = "panic_impl"] |
| || tcx.has_attr(def_id, sym::panic_handler) |
| } |
| |
| fn has_allow_expect_dead_code(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool { |
| let hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
| let lint_level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0; |
| matches!(lint_level, lint::Allow | lint::Expect(_)) |
| } |
| |
| fn has_used_like_attr(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool { |
| tcx.def_kind(def_id).has_codegen_attrs() && { |
| 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. |
| cg_attrs.contains_extern_indicator() |
| || cg_attrs.flags.contains(CodegenFnAttrFlags::USED) |
| || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) |
| } |
| } |
| |
| if has_allow_expect_dead_code(tcx, def_id) { |
| Some(ComesFromAllowExpect::Yes) |
| } else if has_used_like_attr(tcx, def_id) || has_lang_attr(tcx, def_id) { |
| Some(ComesFromAllowExpect::No) |
| } else { |
| None |
| } |
| } |
| |
| // These check_* functions 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 |
| fn check_item<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>, |
| struct_constructors: &mut LocalDefIdMap<LocalDefId>, |
| id: hir::ItemId, |
| ) { |
| let allow_dead_code = has_allow_dead_code_or_lang_attr(tcx, id.owner_id.def_id); |
| if let Some(comes_from_allow) = allow_dead_code { |
| worklist.push((id.owner_id.def_id, comes_from_allow)); |
| } |
| |
| match tcx.def_kind(id.owner_id) { |
| DefKind::Enum => { |
| let item = tcx.hir().item(id); |
| if let hir::ItemKind::Enum(ref enum_def, _) = item.kind { |
| if let Some(comes_from_allow) = allow_dead_code { |
| worklist.extend( |
| enum_def.variants.iter().map(|variant| (variant.def_id, comes_from_allow)), |
| ); |
| } |
| |
| for variant in enum_def.variants { |
| if let Some(ctor_def_id) = variant.data.ctor_def_id() { |
| struct_constructors.insert(ctor_def_id, variant.def_id); |
| } |
| } |
| } |
| } |
| DefKind::Impl { of_trait } => { |
| if of_trait { |
| worklist.push((id.owner_id.def_id, ComesFromAllowExpect::No)); |
| } |
| |
| // get DefIds from another query |
| let local_def_ids = tcx |
| .associated_item_def_ids(id.owner_id) |
| .iter() |
| .filter_map(|def_id| def_id.as_local()); |
| |
| // And we access the Map here to get HirId from LocalDefId |
| for id in local_def_ids { |
| if of_trait { |
| worklist.push((id, ComesFromAllowExpect::No)); |
| } else if let Some(comes_from_allow) = has_allow_dead_code_or_lang_attr(tcx, id) { |
| worklist.push((id, comes_from_allow)); |
| } |
| } |
| } |
| DefKind::Struct => { |
| let item = tcx.hir().item(id); |
| if let hir::ItemKind::Struct(ref variant_data, _) = item.kind |
| && let Some(ctor_def_id) = variant_data.ctor_def_id() |
| { |
| struct_constructors.insert(ctor_def_id, item.owner_id.def_id); |
| } |
| } |
| DefKind::GlobalAsm => { |
| // global_asm! is always live. |
| worklist.push((id.owner_id.def_id, ComesFromAllowExpect::No)); |
| } |
| _ => {} |
| } |
| } |
| |
| fn check_trait_item( |
| tcx: TyCtxt<'_>, |
| worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>, |
| id: hir::TraitItemId, |
| ) { |
| use hir::TraitItemKind::{Const, Fn}; |
| if matches!(tcx.def_kind(id.owner_id), DefKind::AssocConst | DefKind::AssocFn) { |
| let trait_item = tcx.hir().trait_item(id); |
| if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_))) |
| && let Some(comes_from_allow) = |
| has_allow_dead_code_or_lang_attr(tcx, trait_item.owner_id.def_id) |
| { |
| worklist.push((trait_item.owner_id.def_id, comes_from_allow)); |
| } |
| } |
| } |
| |
| fn check_foreign_item( |
| tcx: TyCtxt<'_>, |
| worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>, |
| id: hir::ForeignItemId, |
| ) { |
| if matches!(tcx.def_kind(id.owner_id), DefKind::Static(_) | DefKind::Fn) |
| && let Some(comes_from_allow) = has_allow_dead_code_or_lang_attr(tcx, id.owner_id.def_id) |
| { |
| worklist.push((id.owner_id.def_id, comes_from_allow)); |
| } |
| } |
| |
| fn create_and_seed_worklist( |
| tcx: TyCtxt<'_>, |
| ) -> (Vec<(LocalDefId, ComesFromAllowExpect)>, LocalDefIdMap<LocalDefId>) { |
| let effective_visibilities = &tcx.effective_visibilities(()); |
| // see `MarkSymbolVisitor::struct_constructors` |
| let mut struct_constructors = Default::default(); |
| let mut worklist = effective_visibilities |
| .iter() |
| .filter_map(|(&id, effective_vis)| { |
| effective_vis |
| .is_public_at_level(Level::Reachable) |
| .then_some(id) |
| .map(|id| (id, ComesFromAllowExpect::No)) |
| }) |
| // Seed entry point |
| .chain( |
| tcx.entry_fn(()) |
| .and_then(|(def_id, _)| def_id.as_local().map(|id| (id, ComesFromAllowExpect::No))), |
| ) |
| .collect::<Vec<_>>(); |
| |
| let crate_items = tcx.hir_crate_items(()); |
| for id in crate_items.items() { |
| check_item(tcx, &mut worklist, &mut struct_constructors, id); |
| } |
| |
| for id in crate_items.trait_items() { |
| check_trait_item(tcx, &mut worklist, id); |
| } |
| |
| for id in crate_items.foreign_items() { |
| check_foreign_item(tcx, &mut worklist, id); |
| } |
| |
| (worklist, struct_constructors) |
| } |
| |
| fn live_symbols_and_ignored_derived_traits( |
| tcx: TyCtxt<'_>, |
| (): (), |
| ) -> (LocalDefIdSet, LocalDefIdMap<Vec<(DefId, DefId)>>) { |
| let (worklist, struct_constructors) = create_and_seed_worklist(tcx); |
| let mut symbol_visitor = MarkSymbolVisitor { |
| worklist, |
| tcx, |
| maybe_typeck_results: None, |
| live_symbols: Default::default(), |
| repr_has_repr_c: false, |
| repr_has_repr_simd: false, |
| in_pat: false, |
| ignore_variant_stack: vec![], |
| struct_constructors, |
| ignored_derived_traits: Default::default(), |
| }; |
| symbol_visitor.mark_live_symbols(); |
| (symbol_visitor.live_symbols, symbol_visitor.ignored_derived_traits) |
| } |
| |
| struct DeadItem { |
| def_id: LocalDefId, |
| name: Symbol, |
| level: lint::Level, |
| } |
| |
| struct DeadVisitor<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| live_symbols: &'tcx LocalDefIdSet, |
| ignored_derived_traits: &'tcx LocalDefIdMap<Vec<(DefId, DefId)>>, |
| } |
| |
| enum ShouldWarnAboutField { |
| Yes(bool), // positional? |
| No, |
| } |
| |
| impl<'tcx> DeadVisitor<'tcx> { |
| fn should_warn_about_field(&mut self, field: &ty::FieldDef) -> ShouldWarnAboutField { |
| if self.live_symbols.contains(&field.did.expect_local()) { |
| return ShouldWarnAboutField::No; |
| } |
| let field_type = self.tcx.type_of(field.did).instantiate_identity(); |
| if field_type.is_phantom_data() { |
| return ShouldWarnAboutField::No; |
| } |
| let is_positional = field.name.as_str().starts_with(|c: char| c.is_ascii_digit()); |
| if is_positional |
| && self |
| .tcx |
| .layout_of(self.tcx.param_env(field.did).and(field_type)) |
| .map_or(true, |layout| layout.is_zst()) |
| { |
| return ShouldWarnAboutField::No; |
| } |
| ShouldWarnAboutField::Yes(is_positional) |
| } |
| |
| // # Panics |
| // All `dead_codes` must have the same lint level, otherwise we will intentionally ICE. |
| // This is because we emit a multi-spanned lint using the lint level of the `dead_codes`'s |
| // first local def id. |
| // Prefer calling `Self.warn_dead_code` or `Self.warn_dead_code_grouped_by_lint_level` |
| // since those methods group by lint level before calling this method. |
| fn lint_at_single_level( |
| &self, |
| dead_codes: &[LocalDefId], |
| participle: &str, |
| parent_item: Option<LocalDefId>, |
| is_positional: bool, |
| ) { |
| let Some(&first_id) = dead_codes.first() else { |
| return; |
| }; |
| let tcx = self.tcx; |
| |
| let first_hir_id = tcx.hir().local_def_id_to_hir_id(first_id); |
| let first_lint_level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, first_hir_id).0; |
| assert!(dead_codes.iter().skip(1).all(|id| { |
| let hir_id = tcx.hir().local_def_id_to_hir_id(*id); |
| let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0; |
| level == first_lint_level |
| })); |
| |
| let names: Vec<_> = |
| dead_codes.iter().map(|&def_id| tcx.item_name(def_id.to_def_id())).collect(); |
| let spans: Vec<_> = dead_codes |
| .iter() |
| .map(|&def_id| match tcx.def_ident_span(def_id) { |
| Some(s) => s.with_ctxt(tcx.def_span(def_id).ctxt()), |
| None => tcx.def_span(def_id), |
| }) |
| .collect(); |
| |
| let descr = tcx.def_descr(first_id.to_def_id()); |
| // `impl` blocks are "batched" and (unlike other batching) might |
| // contain different kinds of associated items. |
| let descr = if dead_codes.iter().any(|did| tcx.def_descr(did.to_def_id()) != descr) { |
| "associated item" |
| } else { |
| descr |
| }; |
| let num = dead_codes.len(); |
| let multiple = num > 6; |
| let name_list = names.into(); |
| |
| let lint = if is_positional { |
| lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS |
| } else { |
| lint::builtin::DEAD_CODE |
| }; |
| |
| let parent_info = if let Some(parent_item) = parent_item { |
| let parent_descr = tcx.def_descr(parent_item.to_def_id()); |
| let span = if let DefKind::Impl { .. } = tcx.def_kind(parent_item) { |
| tcx.def_span(parent_item) |
| } else { |
| tcx.def_ident_span(parent_item).unwrap() |
| }; |
| Some(ParentInfo { num, descr, parent_descr, span }) |
| } else { |
| None |
| }; |
| |
| let encl_def_id = parent_item.unwrap_or(first_id); |
| let ignored_derived_impls = |
| if let Some(ign_traits) = self.ignored_derived_traits.get(&encl_def_id) { |
| let trait_list = ign_traits |
| .iter() |
| .map(|(trait_id, _)| self.tcx.item_name(*trait_id)) |
| .collect::<Vec<_>>(); |
| let trait_list_len = trait_list.len(); |
| Some(IgnoredDerivedImpls { |
| name: self.tcx.item_name(encl_def_id.to_def_id()), |
| trait_list: trait_list.into(), |
| trait_list_len, |
| }) |
| } else { |
| None |
| }; |
| |
| let diag = if is_positional { |
| MultipleDeadCodes::UnusedTupleStructFields { |
| multiple, |
| num, |
| descr, |
| participle, |
| name_list, |
| change_fields_suggestion: ChangeFieldsToBeOfUnitType { num, spans: spans.clone() }, |
| parent_info, |
| ignored_derived_impls, |
| } |
| } else { |
| MultipleDeadCodes::DeadCodes { |
| multiple, |
| num, |
| descr, |
| participle, |
| name_list, |
| parent_info, |
| ignored_derived_impls, |
| } |
| }; |
| |
| self.tcx.emit_spanned_lint(lint, first_hir_id, MultiSpan::from_spans(spans), diag); |
| } |
| |
| fn warn_multiple( |
| &self, |
| def_id: LocalDefId, |
| participle: &str, |
| dead_codes: Vec<DeadItem>, |
| is_positional: bool, |
| ) { |
| let mut dead_codes = dead_codes |
| .iter() |
| .filter(|v| !v.name.as_str().starts_with('_')) |
| .collect::<Vec<&DeadItem>>(); |
| if dead_codes.is_empty() { |
| return; |
| } |
| dead_codes.sort_by_key(|v| v.level); |
| for (_, group) in &dead_codes.into_iter().group_by(|v| v.level) { |
| self.lint_at_single_level( |
| &group.map(|v| v.def_id).collect::<Vec<_>>(), |
| participle, |
| Some(def_id), |
| is_positional, |
| ); |
| } |
| } |
| |
| fn warn_dead_code(&mut self, id: LocalDefId, participle: &str) { |
| self.lint_at_single_level(&[id], participle, None, false); |
| } |
| |
| fn check_definition(&mut self, def_id: LocalDefId) { |
| if self.is_live_code(def_id) { |
| return; |
| } |
| match self.tcx.def_kind(def_id) { |
| DefKind::AssocConst |
| | DefKind::AssocFn |
| | DefKind::Fn |
| | DefKind::Static(_) |
| | DefKind::Const |
| | DefKind::TyAlias |
| | DefKind::Enum |
| | DefKind::Union |
| | DefKind::ForeignTy => self.warn_dead_code(def_id, "used"), |
| DefKind::Struct => self.warn_dead_code(def_id, "constructed"), |
| DefKind::Variant | DefKind::Field => bug!("should be handled specially"), |
| _ => {} |
| } |
| } |
| |
| fn is_live_code(&self, def_id: LocalDefId) -> bool { |
| // if we cannot get a name for the item, then we just assume that it is |
| // live. I mean, we can't really emit a lint. |
| let Some(name) = self.tcx.opt_item_name(def_id.to_def_id()) else { |
| return true; |
| }; |
| |
| self.live_symbols.contains(&def_id) || name.as_str().starts_with('_') |
| } |
| } |
| |
| fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) { |
| let (live_symbols, ignored_derived_traits) = tcx.live_symbols_and_ignored_derived_traits(()); |
| let mut visitor = DeadVisitor { tcx, live_symbols, ignored_derived_traits }; |
| |
| let module_items = tcx.hir_module_items(module); |
| |
| for item in module_items.items() { |
| if let hir::ItemKind::Impl(impl_item) = tcx.hir().item(item).kind { |
| let mut dead_items = Vec::new(); |
| for item in impl_item.items { |
| let def_id = item.id.owner_id.def_id; |
| if !visitor.is_live_code(def_id) { |
| let name = tcx.item_name(def_id.to_def_id()); |
| let hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
| let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0; |
| |
| dead_items.push(DeadItem { def_id, name, level }) |
| } |
| } |
| visitor.warn_multiple(item.owner_id.def_id, "used", dead_items, false); |
| } |
| |
| if !live_symbols.contains(&item.owner_id.def_id) { |
| let parent = tcx.local_parent(item.owner_id.def_id); |
| if parent != module.to_local_def_id() && !live_symbols.contains(&parent) { |
| // We already have diagnosed something. |
| continue; |
| } |
| visitor.check_definition(item.owner_id.def_id); |
| continue; |
| } |
| |
| let def_kind = tcx.def_kind(item.owner_id); |
| if let DefKind::Struct | DefKind::Union | DefKind::Enum = def_kind { |
| let adt = tcx.adt_def(item.owner_id); |
| let mut dead_variants = Vec::new(); |
| |
| for variant in adt.variants() { |
| let def_id = variant.def_id.expect_local(); |
| if !live_symbols.contains(&def_id) { |
| // Record to group diagnostics. |
| let hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
| let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0; |
| dead_variants.push(DeadItem { def_id, name: variant.name, level }); |
| continue; |
| } |
| |
| let mut is_positional = false; |
| let dead_fields = variant |
| .fields |
| .iter() |
| .filter_map(|field| { |
| let def_id = field.did.expect_local(); |
| let hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
| if let ShouldWarnAboutField::Yes(is_pos) = |
| visitor.should_warn_about_field(&field) |
| { |
| let level = tcx |
| .lint_level_at_node( |
| if is_pos { |
| is_positional = true; |
| lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS |
| } else { |
| lint::builtin::DEAD_CODE |
| }, |
| hir_id, |
| ) |
| .0; |
| Some(DeadItem { def_id, name: field.name, level }) |
| } else { |
| None |
| } |
| }) |
| .collect(); |
| visitor.warn_multiple(def_id, "read", dead_fields, is_positional); |
| } |
| |
| visitor.warn_multiple(item.owner_id.def_id, "constructed", dead_variants, false); |
| } |
| } |
| |
| for foreign_item in module_items.foreign_items() { |
| visitor.check_definition(foreign_item.owner_id.def_id); |
| } |
| |
| // We do not warn trait items. |
| } |
| |
| pub(crate) fn provide(providers: &mut Providers) { |
| *providers = |
| Providers { live_symbols_and_ignored_derived_traits, check_mod_deathness, ..*providers }; |
| } |
