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diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
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+// 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 itertools::Itertools;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::{pluralize, Applicability, MultiSpan};
+use rustc_hir as hir;
+use rustc_hir::def::{CtorOf, DefKind, Res};
+use rustc_hir::def_id::{DefId, LocalDefId};
+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;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::{self, DefIdTree, TyCtxt};
+use rustc_session::lint;
+use rustc_span::symbol::{sym, Symbol};
+use std::mem;
+
+// 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(..)
+ )
+ )
+}
+
+struct MarkSymbolVisitor<'tcx> {
+ worklist: Vec<LocalDefId>,
+ tcx: TyCtxt<'tcx>,
+ maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
+ live_symbols: FxHashSet<LocalDefId>,
+ 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: FxHashMap<LocalDefId, 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: FxHashMap<LocalDefId, 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);
+ }
+ 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::SelfTy { trait_: t, alias_to: 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 => {}
+ }
+ }
+
+ 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>(
+ 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.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 handle_tuple_field_pattern_match(
+ &mut self,
+ lhs: &hir::Pat<'_>,
+ res: Res,
+ pats: &[hir::Pat<'_>],
+ dotdot: Option<usize>,
+ ) {
+ 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 first_n = pats.iter().enumerate().take(dotdot.unwrap_or(pats.len()));
+ let missing = variant.fields.len() - pats.len();
+ let last_n = pats
+ .iter()
+ .enumerate()
+ .skip(dotdot.unwrap_or(pats.len()))
+ .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[idx].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).copied().unwrap_or(id);
+
+ if let Some(node) = self.tcx.hir().find_by_def_id(id) {
+ 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.has_attr(impl_of, sym::automatically_derived) {
+ 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();
+ 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 { def_id, .. }) = node
+ && self.should_ignore_item(def_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.def_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.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);
+ 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.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> {
+ 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 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 = tcx.hir().local_def_id(f.hir_id);
+ if has_repr_c || (f.is_positional() && has_repr_simd) {
+ return Some(def_id);
+ }
+ if !tcx.visibility(f.hir_id.owner).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);
+ }
+ }
+ _ => (),
+ }
+
+ 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: &'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) {
+ // 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(self.tcx.hir().local_def_id(c.hir_id));
+ intravisit::walk_anon_const(self, c);
+
+ self.in_pat = in_pat;
+ }
+}
+
+fn has_allow_dead_code_or_lang_attr_helper(
+ tcx: TyCtxt<'_>,
+ id: hir::HirId,
+ lint: &'static lint::Lint,
+) -> 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);
+ if 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.
+ if cg_attrs.contains_extern_indicator()
+ || cg_attrs.flags.contains(CodegenFnAttrFlags::USED)
+ || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
+ {
+ return true;
+ }
+ }
+
+ tcx.lint_level_at_node(lint, id).0 == lint::Allow
+}
+
+fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
+ has_allow_dead_code_or_lang_attr_helper(tcx, id, lint::builtin::DEAD_CODE)
+}
+
+// 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>,
+ struct_constructors: &mut FxHashMap<LocalDefId, LocalDefId>,
+ id: hir::ItemId,
+) {
+ let allow_dead_code = has_allow_dead_code_or_lang_attr(tcx, id.hir_id());
+ if allow_dead_code {
+ worklist.push(id.def_id);
+ }
+
+ match tcx.def_kind(id.def_id) {
+ DefKind::Enum => {
+ let item = tcx.hir().item(id);
+ if let hir::ItemKind::Enum(ref enum_def, _) = item.kind {
+ let hir = tcx.hir();
+ if allow_dead_code {
+ worklist.extend(
+ enum_def.variants.iter().map(|variant| hir.local_def_id(variant.id)),
+ );
+ }
+
+ for variant in enum_def.variants {
+ if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
+ struct_constructors
+ .insert(hir.local_def_id(ctor_hir_id), hir.local_def_id(variant.id));
+ }
+ }
+ }
+ }
+ DefKind::Impl => {
+ let of_trait = tcx.impl_trait_ref(id.def_id);
+
+ if of_trait.is_some() {
+ worklist.push(id.def_id);
+ }
+
+ // get DefIds from another query
+ let local_def_ids = tcx
+ .associated_item_def_ids(id.def_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.is_some()
+ || has_allow_dead_code_or_lang_attr(tcx, tcx.hir().local_def_id_to_hir_id(id))
+ {
+ worklist.push(id);
+ }
+ }
+ }
+ DefKind::Struct => {
+ let item = tcx.hir().item(id);
+ if let hir::ItemKind::Struct(ref variant_data, _) = item.kind
+ && let Some(ctor_hir_id) = variant_data.ctor_hir_id()
+ {
+ struct_constructors.insert(tcx.hir().local_def_id(ctor_hir_id), item.def_id);
+ }
+ }
+ DefKind::GlobalAsm => {
+ // global_asm! is always live.
+ worklist.push(id.def_id);
+ }
+ _ => {}
+ }
+}
+
+fn check_trait_item<'tcx>(tcx: TyCtxt<'tcx>, worklist: &mut Vec<LocalDefId>, id: hir::TraitItemId) {
+ use hir::TraitItemKind::{Const, Fn};
+ if matches!(tcx.def_kind(id.def_id), DefKind::AssocConst | DefKind::AssocFn) {
+ let trait_item = tcx.hir().trait_item(id);
+ if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_)))
+ && has_allow_dead_code_or_lang_attr(tcx, trait_item.hir_id())
+ {
+ worklist.push(trait_item.def_id);
+ }
+ }
+}
+
+fn check_foreign_item<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ worklist: &mut Vec<LocalDefId>,
+ id: hir::ForeignItemId,
+) {
+ if matches!(tcx.def_kind(id.def_id), DefKind::Static(_) | DefKind::Fn)
+ && has_allow_dead_code_or_lang_attr(tcx, id.hir_id())
+ {
+ worklist.push(id.def_id);
+ }
+}
+
+fn create_and_seed_worklist<'tcx>(
+ tcx: TyCtxt<'tcx>,
+) -> (Vec<LocalDefId>, FxHashMap<LocalDefId, LocalDefId>) {
+ let access_levels = &tcx.privacy_access_levels(());
+ // see `MarkSymbolVisitor::struct_constructors`
+ let mut struct_constructors = Default::default();
+ let mut worklist = access_levels
+ .map
+ .iter()
+ .filter_map(
+ |(&id, &level)| {
+ if level >= privacy::AccessLevel::Reachable { Some(id) } else { None }
+ },
+ )
+ // Seed entry point
+ .chain(tcx.entry_fn(()).and_then(|(def_id, _)| def_id.as_local()))
+ .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>(
+ tcx: TyCtxt<'tcx>,
+ (): (),
+) -> (FxHashSet<LocalDefId>, FxHashMap<LocalDefId, 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: FxHashMap::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 FxHashSet<LocalDefId>,
+ ignored_derived_traits: &'tcx FxHashMap<LocalDefId, 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);
+ 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<LocalDefId>,
+ is_positional: bool,
+ ) {
+ if let Some(&first_id) = dead_codes.first() {
+ let tcx = self.tcx;
+ let names: Vec<_> = dead_codes
+ .iter()
+ .map(|&def_id| tcx.item_name(def_id.to_def_id()).to_string())
+ .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();
+
+ tcx.struct_span_lint_hir(
+ if is_positional {
+ lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS
+ } else {
+ lint::builtin::DEAD_CODE
+ },
+ tcx.hir().local_def_id_to_hir_id(first_id),
+ MultiSpan::from_spans(spans.clone()),
+ |lint| {
+ let descr = tcx.def_kind(first_id).descr(first_id.to_def_id());
+ let span_len = dead_codes.len();
+ let names = match &names[..] {
+ _ if span_len > 6 => String::new(),
+ [name] => format!("`{name}` "),
+ [names @ .., last] => {
+ format!(
+ "{} and `{last}` ",
+ names.iter().map(|name| format!("`{name}`")).join(", ")
+ )
+ }
+ [] => unreachable!(),
+ };
+ let mut err = lint.build(&format!(
+ "{these}{descr}{s} {names}{are} never {participle}",
+ these = if span_len > 6 { "multiple " } else { "" },
+ s = pluralize!(span_len),
+ are = pluralize!("is", span_len),
+ ));
+
+ if is_positional {
+ err.multipart_suggestion(
+ &format!(
+ "consider changing the field{s} to be of unit type to \
+ suppress this warning while preserving the field \
+ numbering, or remove the field{s}",
+ s = pluralize!(span_len)
+ ),
+ spans.iter().map(|sp| (*sp, "()".to_string())).collect(),
+ // "HasPlaceholders" because applying this fix by itself isn't
+ // enough: All constructor calls have to be adjusted as well
+ Applicability::HasPlaceholders,
+ );
+ }
+
+ if let Some(parent_item) = parent_item {
+ let parent_descr = tcx.def_kind(parent_item).descr(parent_item.to_def_id());
+ err.span_label(
+ tcx.def_ident_span(parent_item).unwrap(),
+ format!("{descr}{s} in this {parent_descr}", s = pluralize!(span_len)),
+ );
+ }
+
+ let encl_def_id = parent_item.unwrap_or(first_id);
+ if let Some(ign_traits) = self.ignored_derived_traits.get(&encl_def_id) {
+ let traits_str = ign_traits
+ .iter()
+ .map(|(trait_id, _)| format!("`{}`", self.tcx.item_name(*trait_id)))
+ .collect::<Vec<_>>()
+ .join(" and ");
+ let plural_s = pluralize!(ign_traits.len());
+ let article = if ign_traits.len() > 1 { "" } else { "a " };
+ let is_are = if ign_traits.len() > 1 { "these are" } else { "this is" };
+ let msg = format!(
+ "`{}` has {}derived impl{} for the trait{} {}, but {} \
+ intentionally ignored during dead code analysis",
+ self.tcx.item_name(encl_def_id.to_def_id()),
+ article,
+ plural_s,
+ plural_s,
+ traits_str,
+ is_are
+ );
+ err.note(&msg);
+ }
+ err.emit();
+ },
+ );
+ }
+ }
+
+ fn warn_dead_fields_and_variants(
+ &self,
+ def_id: LocalDefId,
+ participle: &str,
+ dead_codes: Vec<DeadVariant>,
+ is_positional: bool,
+ ) {
+ let mut dead_codes = dead_codes
+ .iter()
+ .filter(|v| !v.name.as_str().starts_with('_'))
+ .map(|v| v)
+ .collect::<Vec<&DeadVariant>>();
+ 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::<Vec<_>>(),
+ 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.live_symbols.contains(&def_id) {
+ return;
+ }
+ let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
+ if has_allow_dead_code_or_lang_attr(self.tcx, hir_id) {
+ return;
+ }
+ let Some(name) = self.tcx.opt_item_name(def_id.to_def_id()) else {
+ return
+ };
+ if name.as_str().starts_with('_') {
+ 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 check_mod_deathness(tcx: TyCtxt<'_>, module: LocalDefId) {
+ 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 !live_symbols.contains(&item.def_id) {
+ let parent = tcx.local_parent(item.def_id);
+ if parent != module && !live_symbols.contains(&parent) {
+ // We already have diagnosed something.
+ continue;
+ }
+ visitor.check_definition(item.def_id);
+ continue;
+ }
+
+ let def_kind = tcx.def_kind(item.def_id);
+ if let DefKind::Struct | DefKind::Union | DefKind::Enum = def_kind {
+ let adt = tcx.adt_def(item.def_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.def_id, "constructed", dead_variants, false);
+ }
+ }
+
+ for impl_item in module_items.impl_items() {
+ visitor.check_definition(impl_item.def_id);
+ }
+
+ for foreign_item in module_items.foreign_items() {
+ visitor.check_definition(foreign_item.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 };
+}