// 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 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, // maps from tuple struct constructors to tuple struct items struct_constructors: LocalDefIdMap, // 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>, } 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 &index in indices { match current_ty.kind() { ty::Adt(def, subst) => { let field = &def.non_enum_variant().fields[index]; 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[index.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 { 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, 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) { 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::>(); 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>) { 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 DeadVariant { def_id: LocalDefId, name: Symbol, level: lint::Level, } struct DeadVisitor<'tcx> { tcx: TyCtxt<'tcx>, live_symbols: &'tcx LocalDefIdSet, ignored_derived_traits: &'tcx LocalDefIdMap>, } 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) } fn warn_multiple_dead_codes( &self, dead_codes: &[LocalDefId], participle: &str, parent_item: Option, is_positional: bool, ) { let Some(&first_id) = dead_codes.first() else { return; }; let tcx = self.tcx; 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::>(); 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, tcx.hir().local_def_id_to_hir_id(first_id), MultiSpan::from_spans(spans), diag, ); } fn warn_dead_fields_and_variants( &self, def_id: LocalDefId, participle: &str, dead_codes: Vec, is_positional: bool, ) { let mut dead_codes = dead_codes .iter() .filter(|v| !v.name.as_str().starts_with('_')) .collect::>(); 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.warn_multiple_dead_codes( &group.map(|v| v.def_id).collect::>(), participle, Some(def_id), is_positional, ); } } fn warn_dead_code(&mut self, id: LocalDefId, participle: &str) { self.warn_multiple_dead_codes(&[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 did = item.id.owner_id.def_id; if !visitor.is_live_code(did) { dead_items.push(did) } } visitor.warn_multiple_dead_codes( &dead_items, "used", Some(item.owner_id.def_id), 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(DeadVariant { 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(DeadVariant { def_id, name: field.name, level }) } else { None } }) .collect(); visitor.warn_dead_fields_and_variants(def_id, "read", dead_fields, is_positional) } visitor.warn_dead_fields_and_variants( 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 }; }