1 // This implements the dead-code warning pass. It follows middle::reachable
2 // closely. The idea is that all reachable symbols are live, codes called
3 // from live codes are live, and everything else is dead.
5 use itertools::Itertools;
6 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
7 use rustc_errors::{pluralize, MultiSpan};
9 use rustc_hir::def::{CtorOf, DefKind, Res};
10 use rustc_hir::def_id::{DefId, LocalDefId};
11 use rustc_hir::intravisit::{self, Visitor};
12 use rustc_hir::{Node, PatKind, TyKind};
13 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
14 use rustc_middle::middle::privacy;
15 use rustc_middle::ty::query::Providers;
16 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
17 use rustc_session::lint;
18 use rustc_span::symbol::{sym, Symbol};
21 // Any local node that may call something in its body block should be
22 // explored. For example, if it's a live Node::Item that is a
23 // function, then we should explore its block to check for codes that
24 // may need to be marked as live.
25 fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
27 tcx.hir().find_by_def_id(def_id),
31 | Node::ForeignItem(..)
39 struct MarkSymbolVisitor<'tcx> {
40 worklist: Vec<LocalDefId>,
42 maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
43 live_symbols: FxHashSet<LocalDefId>,
44 repr_has_repr_c: bool,
46 ignore_variant_stack: Vec<DefId>,
47 // maps from tuple struct constructors to tuple struct items
48 struct_constructors: FxHashMap<LocalDefId, LocalDefId>,
49 // maps from ADTs to ignored derived traits (e.g. Debug and Clone)
50 // and the span of their respective impl (i.e., part of the derive
52 ignored_derived_traits: FxHashMap<LocalDefId, Vec<(DefId, DefId)>>,
55 impl<'tcx> MarkSymbolVisitor<'tcx> {
56 /// Gets the type-checking results for the current body.
57 /// As this will ICE if called outside bodies, only call when working with
58 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
60 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
61 self.maybe_typeck_results
62 .expect("`MarkSymbolVisitor::typeck_results` called outside of body")
65 fn check_def_id(&mut self, def_id: DefId) {
66 if let Some(def_id) = def_id.as_local() {
67 if should_explore(self.tcx, def_id) || self.struct_constructors.contains_key(&def_id) {
68 self.worklist.push(def_id);
70 self.live_symbols.insert(def_id);
74 fn insert_def_id(&mut self, def_id: DefId) {
75 if let Some(def_id) = def_id.as_local() {
76 debug_assert!(!should_explore(self.tcx, def_id));
77 self.live_symbols.insert(def_id);
81 fn handle_res(&mut self, res: Res) {
83 Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::TyAlias, def_id) => {
84 self.check_def_id(def_id);
86 _ if self.in_pat => {}
87 Res::PrimTy(..) | Res::SelfCtor(..) | Res::Local(..) => {}
88 Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => {
89 let variant_id = self.tcx.parent(ctor_def_id);
90 let enum_id = self.tcx.parent(variant_id);
91 self.check_def_id(enum_id);
92 if !self.ignore_variant_stack.contains(&ctor_def_id) {
93 self.check_def_id(variant_id);
96 Res::Def(DefKind::Variant, variant_id) => {
97 let enum_id = self.tcx.parent(variant_id);
98 self.check_def_id(enum_id);
99 if !self.ignore_variant_stack.contains(&variant_id) {
100 self.check_def_id(variant_id);
103 Res::Def(_, def_id) => self.check_def_id(def_id),
104 Res::SelfTy { trait_: t, alias_to: i } => {
106 self.check_def_id(t);
108 if let Some((i, _)) = i {
109 self.check_def_id(i);
112 Res::ToolMod | Res::NonMacroAttr(..) | Res::Err => {}
116 fn lookup_and_handle_method(&mut self, id: hir::HirId) {
117 if let Some(def_id) = self.typeck_results().type_dependent_def_id(id) {
118 self.check_def_id(def_id);
120 bug!("no type-dependent def for method");
124 fn handle_field_access(&mut self, lhs: &hir::Expr<'_>, hir_id: hir::HirId) {
125 match self.typeck_results().expr_ty_adjusted(lhs).kind() {
127 let index = self.tcx.field_index(hir_id, self.typeck_results());
128 self.insert_def_id(def.non_enum_variant().fields[index].did);
131 _ => span_bug!(lhs.span, "named field access on non-ADT"),
135 #[allow(dead_code)] // FIXME(81658): should be used + lint reinstated after #83171 relands.
136 fn handle_assign(&mut self, expr: &'tcx hir::Expr<'tcx>) {
139 .expr_adjustments(expr)
141 .any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(_)))
143 self.visit_expr(expr);
144 } else if let hir::ExprKind::Field(base, ..) = expr.kind {
145 // Ignore write to field
146 self.handle_assign(base);
148 self.visit_expr(expr);
152 #[allow(dead_code)] // FIXME(81658): should be used + lint reinstated after #83171 relands.
153 fn check_for_self_assign(&mut self, assign: &'tcx hir::Expr<'tcx>) {
154 fn check_for_self_assign_helper<'tcx>(
155 typeck_results: &'tcx ty::TypeckResults<'tcx>,
156 lhs: &'tcx hir::Expr<'tcx>,
157 rhs: &'tcx hir::Expr<'tcx>,
159 match (&lhs.kind, &rhs.kind) {
160 (hir::ExprKind::Path(ref qpath_l), hir::ExprKind::Path(ref qpath_r)) => {
161 if let (Res::Local(id_l), Res::Local(id_r)) = (
162 typeck_results.qpath_res(qpath_l, lhs.hir_id),
163 typeck_results.qpath_res(qpath_r, rhs.hir_id),
171 (hir::ExprKind::Field(lhs_l, ident_l), hir::ExprKind::Field(lhs_r, ident_r)) => {
172 if ident_l == ident_r {
173 return check_for_self_assign_helper(typeck_results, lhs_l, lhs_r);
183 if let hir::ExprKind::Assign(lhs, rhs, _) = assign.kind
184 && check_for_self_assign_helper(self.typeck_results(), lhs, rhs)
185 && !assign.span.from_expansion()
187 let is_field_assign = matches!(lhs.kind, hir::ExprKind::Field(..));
188 self.tcx.struct_span_lint_hir(
189 lint::builtin::DEAD_CODE,
194 "useless assignment of {} of type `{}` to itself",
195 if is_field_assign { "field" } else { "variable" },
196 self.typeck_results().expr_ty(lhs),
204 fn handle_field_pattern_match(
208 pats: &[hir::PatField<'_>],
210 let variant = match self.typeck_results().node_type(lhs.hir_id).kind() {
211 ty::Adt(adt, _) => adt.variant_of_res(res),
212 _ => span_bug!(lhs.span, "non-ADT in struct pattern"),
215 if let PatKind::Wild = pat.pat.kind {
218 let index = self.tcx.field_index(pat.hir_id, self.typeck_results());
219 self.insert_def_id(variant.fields[index].did);
223 fn mark_live_symbols(&mut self) {
224 let mut scanned = FxHashSet::default();
225 while let Some(id) = self.worklist.pop() {
226 if !scanned.insert(id) {
230 // in the case of tuple struct constructors we want to check the item, not the generated
231 // tuple struct constructor function
232 let id = self.struct_constructors.get(&id).copied().unwrap_or(id);
234 if let Some(node) = self.tcx.hir().find_by_def_id(id) {
235 self.live_symbols.insert(id);
236 self.visit_node(node);
241 /// Automatically generated items marked with `rustc_trivial_field_reads`
242 /// will be ignored for the purposes of dead code analysis (see PR #85200
244 fn should_ignore_item(&mut self, def_id: DefId) -> bool {
245 if let Some(impl_of) = self.tcx.impl_of_method(def_id) {
246 if !self.tcx.has_attr(impl_of, sym::automatically_derived) {
250 if let Some(trait_of) = self.tcx.trait_id_of_impl(impl_of)
251 && self.tcx.has_attr(trait_of, sym::rustc_trivial_field_reads)
253 let trait_ref = self.tcx.impl_trait_ref(impl_of).unwrap();
254 if let ty::Adt(adt_def, _) = trait_ref.self_ty().kind()
255 && let Some(adt_def_id) = adt_def.did().as_local()
257 self.ignored_derived_traits
260 .push((trait_of, impl_of));
269 fn visit_node(&mut self, node: Node<'tcx>) {
270 if let Node::ImplItem(hir::ImplItem { def_id, .. }) = node
271 && self.should_ignore_item(def_id.to_def_id())
276 let had_repr_c = self.repr_has_repr_c;
277 self.repr_has_repr_c = false;
279 Node::Item(item) => match item.kind {
280 hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
281 let def = self.tcx.adt_def(item.def_id);
282 self.repr_has_repr_c = def.repr().c();
284 intravisit::walk_item(self, &item)
286 hir::ItemKind::ForeignMod { .. } => {}
287 _ => intravisit::walk_item(self, &item),
289 Node::TraitItem(trait_item) => {
290 intravisit::walk_trait_item(self, trait_item);
292 Node::ImplItem(impl_item) => {
293 let item = self.tcx.local_parent(impl_item.def_id);
294 if self.tcx.impl_trait_ref(item).is_none() {
295 //// If it's a type whose items are live, then it's live, too.
296 //// This is done to handle the case where, for example, the static
297 //// method of a private type is used, but the type itself is never
298 //// called directly.
299 let self_ty = self.tcx.type_of(item);
300 match *self_ty.kind() {
301 ty::Adt(def, _) => self.check_def_id(def.did()),
302 ty::Foreign(did) => self.check_def_id(did),
303 ty::Dynamic(data, ..) => {
304 if let Some(def_id) = data.principal_def_id() {
305 self.check_def_id(def_id)
311 intravisit::walk_impl_item(self, impl_item);
313 Node::ForeignItem(foreign_item) => {
314 intravisit::walk_foreign_item(self, &foreign_item);
318 self.repr_has_repr_c = had_repr_c;
321 fn mark_as_used_if_union(&mut self, adt: ty::AdtDef<'tcx>, fields: &[hir::ExprField<'_>]) {
322 if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did().is_local() {
323 for field in fields {
324 let index = self.tcx.field_index(field.hir_id, self.typeck_results());
325 self.insert_def_id(adt.non_enum_variant().fields[index].did);
331 impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
332 fn visit_nested_body(&mut self, body: hir::BodyId) {
333 let old_maybe_typeck_results =
334 self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
335 let body = self.tcx.hir().body(body);
336 self.visit_body(body);
337 self.maybe_typeck_results = old_maybe_typeck_results;
340 fn visit_variant_data(
342 def: &'tcx hir::VariantData<'tcx>,
344 _: &hir::Generics<'_>,
349 let has_repr_c = self.repr_has_repr_c;
350 let live_fields = def.fields().iter().filter_map(|f| {
351 let def_id = tcx.hir().local_def_id(f.hir_id);
355 if !tcx.visibility(f.hir_id.owner).is_public() {
358 if tcx.visibility(def_id).is_public() { Some(def_id) } else { None }
360 self.live_symbols.extend(live_fields);
362 intravisit::walk_struct_def(self, def);
365 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
367 hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
368 let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
369 self.handle_res(res);
371 hir::ExprKind::MethodCall(..) => {
372 self.lookup_and_handle_method(expr.hir_id);
374 hir::ExprKind::Field(ref lhs, ..) => {
375 self.handle_field_access(&lhs, expr.hir_id);
377 hir::ExprKind::Struct(ref qpath, ref fields, _) => {
378 let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
379 self.handle_res(res);
380 if let ty::Adt(adt, _) = self.typeck_results().expr_ty(expr).kind() {
381 self.mark_as_used_if_union(*adt, fields);
387 intravisit::walk_expr(self, expr);
390 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
391 // Inside the body, ignore constructions of variants
392 // necessary for the pattern to match. Those construction sites
393 // can't be reached unless the variant is constructed elsewhere.
394 let len = self.ignore_variant_stack.len();
395 self.ignore_variant_stack.extend(arm.pat.necessary_variants());
396 intravisit::walk_arm(self, arm);
397 self.ignore_variant_stack.truncate(len);
400 fn visit_pat(&mut self, pat: &'tcx hir::Pat<'tcx>) {
403 PatKind::Struct(ref path, ref fields, _) => {
404 let res = self.typeck_results().qpath_res(path, pat.hir_id);
405 self.handle_field_pattern_match(pat, res, fields);
407 PatKind::Path(ref qpath) => {
408 let res = self.typeck_results().qpath_res(qpath, pat.hir_id);
409 self.handle_res(res);
414 intravisit::walk_pat(self, pat);
418 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
419 self.handle_res(path.res);
420 intravisit::walk_path(self, path);
423 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
424 if let TyKind::OpaqueDef(item_id, _) = ty.kind {
425 let item = self.tcx.hir().item(item_id);
426 intravisit::walk_item(self, item);
428 intravisit::walk_ty(self, ty);
431 fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
432 // When inline const blocks are used in pattern position, paths
433 // referenced by it should be considered as used.
434 let in_pat = mem::replace(&mut self.in_pat, false);
436 self.live_symbols.insert(self.tcx.hir().local_def_id(c.hir_id));
437 intravisit::walk_anon_const(self, c);
439 self.in_pat = in_pat;
443 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
444 let attrs = tcx.hir().attrs(id);
445 if tcx.sess.contains_name(attrs, sym::lang) {
449 // Stable attribute for #[lang = "panic_impl"]
450 if tcx.sess.contains_name(attrs, sym::panic_handler) {
454 // (To be) stable attribute for #[lang = "oom"]
455 if tcx.sess.contains_name(attrs, sym::alloc_error_handler) {
459 let def_id = tcx.hir().local_def_id(id);
460 if tcx.def_kind(def_id).has_codegen_attrs() {
461 let cg_attrs = tcx.codegen_fn_attrs(def_id);
463 // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
464 // forcefully, e.g., for placing it in a specific section.
465 if cg_attrs.contains_extern_indicator()
466 || cg_attrs.flags.contains(CodegenFnAttrFlags::USED)
467 || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
473 tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
476 // These check_* functions seeds items that
477 // 1) We want to explicitly consider as live:
478 // * Item annotated with #[allow(dead_code)]
479 // - This is done so that if we want to suppress warnings for a
480 // group of dead functions, we only have to annotate the "root".
481 // For example, if both `f` and `g` are dead and `f` calls `g`,
482 // then annotating `f` with `#[allow(dead_code)]` will suppress
483 // warning for both `f` and `g`.
484 // * Item annotated with #[lang=".."]
485 // - This is because lang items are always callable from elsewhere.
487 // 2) We are not sure to be live or not
488 // * Implementations of traits and trait methods
491 worklist: &mut Vec<LocalDefId>,
492 struct_constructors: &mut FxHashMap<LocalDefId, LocalDefId>,
495 let allow_dead_code = has_allow_dead_code_or_lang_attr(tcx, id.hir_id());
497 worklist.push(id.def_id);
500 match tcx.def_kind(id.def_id) {
502 let item = tcx.hir().item(id);
503 if let hir::ItemKind::Enum(ref enum_def, _) = item.kind {
507 enum_def.variants.iter().map(|variant| hir.local_def_id(variant.id)),
511 for variant in enum_def.variants {
512 if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
514 .insert(hir.local_def_id(ctor_hir_id), hir.local_def_id(variant.id));
520 let of_trait = tcx.impl_trait_ref(id.def_id);
522 if of_trait.is_some() {
523 worklist.push(id.def_id);
526 // get DefIds from another query
527 let local_def_ids = tcx
528 .associated_item_def_ids(id.def_id)
530 .filter_map(|def_id| def_id.as_local());
532 // And we access the Map here to get HirId from LocalDefId
533 for id in local_def_ids {
534 if of_trait.is_some()
535 || has_allow_dead_code_or_lang_attr(tcx, tcx.hir().local_def_id_to_hir_id(id))
542 let item = tcx.hir().item(id);
543 if let hir::ItemKind::Struct(ref variant_data, _) = item.kind
544 && let Some(ctor_hir_id) = variant_data.ctor_hir_id()
546 struct_constructors.insert(tcx.hir().local_def_id(ctor_hir_id), item.def_id);
549 DefKind::GlobalAsm => {
550 // global_asm! is always live.
551 worklist.push(id.def_id);
557 fn check_trait_item<'tcx>(tcx: TyCtxt<'tcx>, worklist: &mut Vec<LocalDefId>, id: hir::TraitItemId) {
558 use hir::TraitItemKind::{Const, Fn};
559 if matches!(tcx.def_kind(id.def_id), DefKind::AssocConst | DefKind::AssocFn) {
560 let trait_item = tcx.hir().trait_item(id);
561 if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_)))
562 && has_allow_dead_code_or_lang_attr(tcx, trait_item.hir_id())
564 worklist.push(trait_item.def_id);
569 fn check_foreign_item<'tcx>(
571 worklist: &mut Vec<LocalDefId>,
572 id: hir::ForeignItemId,
574 if matches!(tcx.def_kind(id.def_id), DefKind::Static(_) | DefKind::Fn)
575 && has_allow_dead_code_or_lang_attr(tcx, id.hir_id())
577 worklist.push(id.def_id);
581 fn create_and_seed_worklist<'tcx>(
583 ) -> (Vec<LocalDefId>, FxHashMap<LocalDefId, LocalDefId>) {
584 let access_levels = &tcx.privacy_access_levels(());
585 // see `MarkSymbolVisitor::struct_constructors`
586 let mut struct_constructors = Default::default();
587 let mut worklist = access_levels
592 if level >= privacy::AccessLevel::Reachable { Some(id) } else { None }
596 .chain(tcx.entry_fn(()).and_then(|(def_id, _)| def_id.as_local()))
597 .collect::<Vec<_>>();
599 let crate_items = tcx.hir_crate_items(());
600 for id in crate_items.items() {
601 check_item(tcx, &mut worklist, &mut struct_constructors, id);
604 for id in crate_items.trait_items() {
605 check_trait_item(tcx, &mut worklist, id);
608 for id in crate_items.foreign_items() {
609 check_foreign_item(tcx, &mut worklist, id);
612 (worklist, struct_constructors)
615 fn live_symbols_and_ignored_derived_traits<'tcx>(
618 ) -> (FxHashSet<LocalDefId>, FxHashMap<LocalDefId, Vec<(DefId, DefId)>>) {
619 let (worklist, struct_constructors) = create_and_seed_worklist(tcx);
620 let mut symbol_visitor = MarkSymbolVisitor {
623 maybe_typeck_results: None,
624 live_symbols: Default::default(),
625 repr_has_repr_c: false,
627 ignore_variant_stack: vec![],
629 ignored_derived_traits: FxHashMap::default(),
631 symbol_visitor.mark_live_symbols();
632 (symbol_visitor.live_symbols, symbol_visitor.ignored_derived_traits)
641 struct DeadVisitor<'tcx> {
643 live_symbols: &'tcx FxHashSet<LocalDefId>,
644 ignored_derived_traits: &'tcx FxHashMap<LocalDefId, Vec<(DefId, DefId)>>,
647 impl<'tcx> DeadVisitor<'tcx> {
648 fn should_warn_about_field(&mut self, field: &ty::FieldDef) -> bool {
649 if self.live_symbols.contains(&field.did.expect_local()) {
652 let is_positional = field.name.as_str().starts_with(|c: char| c.is_ascii_digit());
656 let field_type = self.tcx.type_of(field.did);
657 !field_type.is_phantom_data()
660 fn warn_multiple_dead_codes(
662 dead_codes: &[LocalDefId],
664 parent_item: Option<LocalDefId>,
666 if let Some(&first_id) = dead_codes.first() {
668 let names: Vec<_> = dead_codes
670 .map(|&def_id| tcx.item_name(def_id.to_def_id()).to_string())
672 let spans = dead_codes
674 .map(|&def_id| match tcx.def_ident_span(def_id) {
675 Some(s) => s.with_ctxt(tcx.def_span(def_id).ctxt()),
676 None => tcx.def_span(def_id),
680 tcx.struct_span_lint_hir(
681 lint::builtin::DEAD_CODE,
682 tcx.hir().local_def_id_to_hir_id(first_id),
683 MultiSpan::from_spans(spans),
685 let descr = tcx.def_kind(first_id).descr(first_id.to_def_id());
686 let span_len = dead_codes.len();
687 let names = match &names[..] {
688 _ if span_len > 6 => String::new(),
689 [name] => format!("`{name}` "),
690 [names @ .., last] => {
693 names.iter().map(|name| format!("`{name}`")).join(", ")
696 [] => unreachable!(),
698 let mut err = lint.build(&format!(
699 "{these}{descr}{s} {names}{are} never {participle}",
700 these = if span_len > 6 { "multiple " } else { "" },
701 s = pluralize!(span_len),
702 are = pluralize!("is", span_len),
705 if let Some(parent_item) = parent_item {
706 let parent_descr = tcx.def_kind(parent_item).descr(parent_item.to_def_id());
708 tcx.def_ident_span(parent_item).unwrap(),
709 format!("{descr}{s} in this {parent_descr}", s = pluralize!(span_len)),
713 let encl_def_id = parent_item.unwrap_or(first_id);
714 if let Some(ign_traits) = self.ignored_derived_traits.get(&encl_def_id) {
715 let traits_str = ign_traits
717 .map(|(trait_id, _)| format!("`{}`", self.tcx.item_name(*trait_id)))
720 let plural_s = pluralize!(ign_traits.len());
721 let article = if ign_traits.len() > 1 { "" } else { "a " };
722 let is_are = if ign_traits.len() > 1 { "these are" } else { "this is" };
724 "`{}` has {}derived impl{} for the trait{} {}, but {} \
725 intentionally ignored during dead code analysis",
726 self.tcx.item_name(encl_def_id.to_def_id()),
741 fn warn_dead_fields_and_variants(
745 dead_codes: Vec<DeadVariant>,
747 let mut dead_codes = dead_codes
749 .filter(|v| !v.name.as_str().starts_with('_'))
751 .collect::<Vec<&DeadVariant>>();
752 if dead_codes.is_empty() {
755 dead_codes.sort_by_key(|v| v.level);
756 for (_, group) in &dead_codes.into_iter().group_by(|v| v.level) {
757 self.warn_multiple_dead_codes(
758 &group.map(|v| v.def_id).collect::<Vec<_>>(),
765 fn warn_dead_code(&mut self, id: LocalDefId, participle: &str) {
766 self.warn_multiple_dead_codes(&[id], participle, None);
769 fn check_definition(&mut self, def_id: LocalDefId) {
770 if self.live_symbols.contains(&def_id) {
773 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
774 if has_allow_dead_code_or_lang_attr(self.tcx, hir_id) {
777 let Some(name) = self.tcx.opt_item_name(def_id.to_def_id()) else {
780 if name.as_str().starts_with('_') {
783 match self.tcx.def_kind(def_id) {
792 | DefKind::ForeignTy => self.warn_dead_code(def_id, "used"),
793 DefKind::Struct => self.warn_dead_code(def_id, "constructed"),
794 DefKind::Variant | DefKind::Field => bug!("should be handled specially"),
800 fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalDefId) {
801 let (live_symbols, ignored_derived_traits) = tcx.live_symbols_and_ignored_derived_traits(());
802 let mut visitor = DeadVisitor { tcx, live_symbols, ignored_derived_traits };
804 let module_items = tcx.hir_module_items(module);
806 for item in module_items.items() {
807 if !live_symbols.contains(&item.def_id) {
808 let parent = tcx.local_parent(item.def_id);
809 if parent != module && !live_symbols.contains(&parent) {
810 // We already have diagnosed something.
813 visitor.check_definition(item.def_id);
817 let def_kind = tcx.def_kind(item.def_id);
818 if let DefKind::Struct | DefKind::Union | DefKind::Enum = def_kind {
819 let adt = tcx.adt_def(item.def_id);
820 let mut dead_variants = Vec::new();
822 for variant in adt.variants() {
823 let def_id = variant.def_id.expect_local();
824 if !live_symbols.contains(&def_id) {
825 // Record to group diagnostics.
826 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
827 let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
828 dead_variants.push(DeadVariant { def_id, name: variant.name, level });
832 let dead_fields = variant
835 .filter_map(|field| {
836 let def_id = field.did.expect_local();
837 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
838 if visitor.should_warn_about_field(&field) {
839 let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
840 Some(DeadVariant { def_id, name: field.name, level })
846 visitor.warn_dead_fields_and_variants(def_id, "read", dead_fields)
849 visitor.warn_dead_fields_and_variants(item.def_id, "constructed", dead_variants);
853 for impl_item in module_items.impl_items() {
854 visitor.check_definition(impl_item.def_id);
857 for foreign_item in module_items.foreign_items() {
858 visitor.check_definition(foreign_item.def_id);
861 // We do not warn trait items.
864 pub(crate) fn provide(providers: &mut Providers) {
866 Providers { live_symbols_and_ignored_derived_traits, check_mod_deathness, ..*providers };