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::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::Level;
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};
22 ChangeFieldsToBeOfUnitType, IgnoredDerivedImpls, MultipleDeadCodes, ParentInfo,
26 // Any local node that may call something in its body block should be
27 // explored. For example, if it's a live Node::Item that is a
28 // function, then we should explore its block to check for codes that
29 // may need to be marked as live.
30 fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
32 tcx.hir().find_by_def_id(def_id),
36 | Node::ForeignItem(..)
44 struct MarkSymbolVisitor<'tcx> {
45 worklist: Vec<LocalDefId>,
47 maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
48 live_symbols: FxHashSet<LocalDefId>,
49 repr_has_repr_c: bool,
50 repr_has_repr_simd: bool,
52 ignore_variant_stack: Vec<DefId>,
53 // maps from tuple struct constructors to tuple struct items
54 struct_constructors: FxHashMap<LocalDefId, LocalDefId>,
55 // maps from ADTs to ignored derived traits (e.g. Debug and Clone)
56 // and the span of their respective impl (i.e., part of the derive
58 ignored_derived_traits: FxHashMap<LocalDefId, Vec<(DefId, DefId)>>,
61 impl<'tcx> MarkSymbolVisitor<'tcx> {
62 /// Gets the type-checking results for the current body.
63 /// As this will ICE if called outside bodies, only call when working with
64 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
66 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
67 self.maybe_typeck_results
68 .expect("`MarkSymbolVisitor::typeck_results` called outside of body")
71 fn check_def_id(&mut self, def_id: DefId) {
72 if let Some(def_id) = def_id.as_local() {
73 if should_explore(self.tcx, def_id) || self.struct_constructors.contains_key(&def_id) {
74 self.worklist.push(def_id);
76 self.live_symbols.insert(def_id);
80 fn insert_def_id(&mut self, def_id: DefId) {
81 if let Some(def_id) = def_id.as_local() {
82 debug_assert!(!should_explore(self.tcx, def_id));
83 self.live_symbols.insert(def_id);
87 fn handle_res(&mut self, res: Res) {
89 Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::TyAlias, def_id) => {
90 self.check_def_id(def_id);
92 _ if self.in_pat => {}
93 Res::PrimTy(..) | Res::SelfCtor(..) | Res::Local(..) => {}
94 Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => {
95 let variant_id = self.tcx.parent(ctor_def_id);
96 let enum_id = self.tcx.parent(variant_id);
97 self.check_def_id(enum_id);
98 if !self.ignore_variant_stack.contains(&ctor_def_id) {
99 self.check_def_id(variant_id);
102 Res::Def(DefKind::Variant, variant_id) => {
103 let enum_id = self.tcx.parent(variant_id);
104 self.check_def_id(enum_id);
105 if !self.ignore_variant_stack.contains(&variant_id) {
106 self.check_def_id(variant_id);
109 Res::Def(_, def_id) => self.check_def_id(def_id),
110 Res::SelfTyParam { trait_: t } => self.check_def_id(t),
111 Res::SelfTyAlias { alias_to: i, .. } => 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.typeck_results().field_index(hir_id);
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.emit_spanned_lint(
189 lint::builtin::DEAD_CODE,
192 UselessAssignment { is_field_assign, ty: self.typeck_results().expr_ty(lhs) }
197 fn handle_field_pattern_match(
201 pats: &[hir::PatField<'_>],
203 let variant = match self.typeck_results().node_type(lhs.hir_id).kind() {
204 ty::Adt(adt, _) => adt.variant_of_res(res),
205 _ => span_bug!(lhs.span, "non-ADT in struct pattern"),
208 if let PatKind::Wild = pat.pat.kind {
211 let index = self.typeck_results().field_index(pat.hir_id);
212 self.insert_def_id(variant.fields[index].did);
216 fn handle_tuple_field_pattern_match(
220 pats: &[hir::Pat<'_>],
221 dotdot: hir::DotDotPos,
223 let variant = match self.typeck_results().node_type(lhs.hir_id).kind() {
224 ty::Adt(adt, _) => adt.variant_of_res(res),
225 _ => span_bug!(lhs.span, "non-ADT in tuple struct pattern"),
227 let dotdot = dotdot.as_opt_usize().unwrap_or(pats.len());
228 let first_n = pats.iter().enumerate().take(dotdot);
229 let missing = variant.fields.len() - pats.len();
230 let last_n = pats.iter().enumerate().skip(dotdot).map(|(idx, pat)| (idx + missing, pat));
231 for (idx, pat) in first_n.chain(last_n) {
232 if let PatKind::Wild = pat.kind {
235 self.insert_def_id(variant.fields[idx].did);
239 fn mark_live_symbols(&mut self) {
240 let mut scanned = FxHashSet::default();
241 while let Some(id) = self.worklist.pop() {
242 if !scanned.insert(id) {
246 // in the case of tuple struct constructors we want to check the item, not the generated
247 // tuple struct constructor function
248 let id = self.struct_constructors.get(&id).copied().unwrap_or(id);
250 if let Some(node) = self.tcx.hir().find_by_def_id(id) {
251 self.live_symbols.insert(id);
252 self.visit_node(node);
257 /// Automatically generated items marked with `rustc_trivial_field_reads`
258 /// will be ignored for the purposes of dead code analysis (see PR #85200
260 fn should_ignore_item(&mut self, def_id: DefId) -> bool {
261 if let Some(impl_of) = self.tcx.impl_of_method(def_id) {
262 if !self.tcx.has_attr(impl_of, sym::automatically_derived) {
266 if let Some(trait_of) = self.tcx.trait_id_of_impl(impl_of)
267 && self.tcx.has_attr(trait_of, sym::rustc_trivial_field_reads)
269 let trait_ref = self.tcx.impl_trait_ref(impl_of).unwrap().subst_identity();
270 if let ty::Adt(adt_def, _) = trait_ref.self_ty().kind()
271 && let Some(adt_def_id) = adt_def.did().as_local()
273 self.ignored_derived_traits
276 .push((trait_of, impl_of));
285 fn visit_node(&mut self, node: Node<'tcx>) {
286 if let Node::ImplItem(hir::ImplItem { owner_id, .. }) = node
287 && self.should_ignore_item(owner_id.to_def_id())
292 let had_repr_c = self.repr_has_repr_c;
293 let had_repr_simd = self.repr_has_repr_simd;
294 self.repr_has_repr_c = false;
295 self.repr_has_repr_simd = false;
297 Node::Item(item) => match item.kind {
298 hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
299 let def = self.tcx.adt_def(item.owner_id);
300 self.repr_has_repr_c = def.repr().c();
301 self.repr_has_repr_simd = def.repr().simd();
303 intravisit::walk_item(self, &item)
305 hir::ItemKind::ForeignMod { .. } => {}
306 _ => intravisit::walk_item(self, &item),
308 Node::TraitItem(trait_item) => {
309 intravisit::walk_trait_item(self, trait_item);
311 Node::ImplItem(impl_item) => {
312 let item = self.tcx.local_parent(impl_item.owner_id.def_id);
313 if self.tcx.impl_trait_ref(item).is_none() {
314 //// If it's a type whose items are live, then it's live, too.
315 //// This is done to handle the case where, for example, the static
316 //// method of a private type is used, but the type itself is never
317 //// called directly.
318 let self_ty = self.tcx.type_of(item);
319 match *self_ty.kind() {
320 ty::Adt(def, _) => self.check_def_id(def.did()),
321 ty::Foreign(did) => self.check_def_id(did),
322 ty::Dynamic(data, ..) => {
323 if let Some(def_id) = data.principal_def_id() {
324 self.check_def_id(def_id)
330 intravisit::walk_impl_item(self, impl_item);
332 Node::ForeignItem(foreign_item) => {
333 intravisit::walk_foreign_item(self, &foreign_item);
337 self.repr_has_repr_simd = had_repr_simd;
338 self.repr_has_repr_c = had_repr_c;
341 fn mark_as_used_if_union(&mut self, adt: ty::AdtDef<'tcx>, fields: &[hir::ExprField<'_>]) {
342 if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did().is_local() {
343 for field in fields {
344 let index = self.typeck_results().field_index(field.hir_id);
345 self.insert_def_id(adt.non_enum_variant().fields[index].did);
351 impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
352 fn visit_nested_body(&mut self, body: hir::BodyId) {
353 let old_maybe_typeck_results =
354 self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
355 let body = self.tcx.hir().body(body);
356 self.visit_body(body);
357 self.maybe_typeck_results = old_maybe_typeck_results;
360 fn visit_variant_data(&mut self, def: &'tcx hir::VariantData<'tcx>) {
362 let has_repr_c = self.repr_has_repr_c;
363 let has_repr_simd = self.repr_has_repr_simd;
364 let live_fields = def.fields().iter().filter_map(|f| {
365 let def_id = f.def_id;
366 if has_repr_c || (f.is_positional() && has_repr_simd) {
369 if !tcx.visibility(f.hir_id.owner.def_id).is_public() {
372 if tcx.visibility(def_id).is_public() { Some(def_id) } else { None }
374 self.live_symbols.extend(live_fields);
376 intravisit::walk_struct_def(self, def);
379 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
381 hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
382 let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
383 self.handle_res(res);
385 hir::ExprKind::MethodCall(..) => {
386 self.lookup_and_handle_method(expr.hir_id);
388 hir::ExprKind::Field(ref lhs, ..) => {
389 self.handle_field_access(&lhs, expr.hir_id);
391 hir::ExprKind::Struct(ref qpath, ref fields, _) => {
392 let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
393 self.handle_res(res);
394 if let ty::Adt(adt, _) = self.typeck_results().expr_ty(expr).kind() {
395 self.mark_as_used_if_union(*adt, fields);
401 intravisit::walk_expr(self, expr);
404 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
405 // Inside the body, ignore constructions of variants
406 // necessary for the pattern to match. Those construction sites
407 // can't be reached unless the variant is constructed elsewhere.
408 let len = self.ignore_variant_stack.len();
409 self.ignore_variant_stack.extend(arm.pat.necessary_variants());
410 intravisit::walk_arm(self, arm);
411 self.ignore_variant_stack.truncate(len);
414 fn visit_pat(&mut self, pat: &'tcx hir::Pat<'tcx>) {
417 PatKind::Struct(ref path, ref fields, _) => {
418 let res = self.typeck_results().qpath_res(path, pat.hir_id);
419 self.handle_field_pattern_match(pat, res, fields);
421 PatKind::Path(ref qpath) => {
422 let res = self.typeck_results().qpath_res(qpath, pat.hir_id);
423 self.handle_res(res);
425 PatKind::TupleStruct(ref qpath, ref fields, dotdot) => {
426 let res = self.typeck_results().qpath_res(qpath, pat.hir_id);
427 self.handle_tuple_field_pattern_match(pat, res, fields, dotdot);
432 intravisit::walk_pat(self, pat);
436 fn visit_path(&mut self, path: &hir::Path<'tcx>, _: hir::HirId) {
437 self.handle_res(path.res);
438 intravisit::walk_path(self, path);
441 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
442 if let TyKind::OpaqueDef(item_id, _, _) = ty.kind {
443 let item = self.tcx.hir().item(item_id);
444 intravisit::walk_item(self, item);
446 intravisit::walk_ty(self, ty);
449 fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
450 // When inline const blocks are used in pattern position, paths
451 // referenced by it should be considered as used.
452 let in_pat = mem::replace(&mut self.in_pat, false);
454 self.live_symbols.insert(self.tcx.hir().local_def_id(c.hir_id));
455 intravisit::walk_anon_const(self, c);
457 self.in_pat = in_pat;
461 fn has_allow_dead_code_or_lang_attr_helper(
464 lint: &'static lint::Lint,
466 let attrs = tcx.hir().attrs(id);
467 if tcx.sess.contains_name(attrs, sym::lang) {
471 // Stable attribute for #[lang = "panic_impl"]
472 if tcx.sess.contains_name(attrs, sym::panic_handler) {
476 let def_id = tcx.hir().local_def_id(id);
477 if tcx.def_kind(def_id).has_codegen_attrs() {
478 let cg_attrs = tcx.codegen_fn_attrs(def_id);
480 // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
481 // forcefully, e.g., for placing it in a specific section.
482 if cg_attrs.contains_extern_indicator()
483 || cg_attrs.flags.contains(CodegenFnAttrFlags::USED)
484 || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
490 tcx.lint_level_at_node(lint, id).0 == lint::Allow
493 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
494 has_allow_dead_code_or_lang_attr_helper(tcx, id, lint::builtin::DEAD_CODE)
497 // These check_* functions seeds items that
498 // 1) We want to explicitly consider as live:
499 // * Item annotated with #[allow(dead_code)]
500 // - This is done so that if we want to suppress warnings for a
501 // group of dead functions, we only have to annotate the "root".
502 // For example, if both `f` and `g` are dead and `f` calls `g`,
503 // then annotating `f` with `#[allow(dead_code)]` will suppress
504 // warning for both `f` and `g`.
505 // * Item annotated with #[lang=".."]
506 // - This is because lang items are always callable from elsewhere.
508 // 2) We are not sure to be live or not
509 // * Implementations of traits and trait methods
512 worklist: &mut Vec<LocalDefId>,
513 struct_constructors: &mut FxHashMap<LocalDefId, LocalDefId>,
516 let allow_dead_code = has_allow_dead_code_or_lang_attr(tcx, id.hir_id());
518 worklist.push(id.owner_id.def_id);
521 match tcx.def_kind(id.owner_id) {
523 let item = tcx.hir().item(id);
524 if let hir::ItemKind::Enum(ref enum_def, _) = item.kind {
526 worklist.extend(enum_def.variants.iter().map(|variant| variant.def_id));
529 for variant in enum_def.variants {
530 if let Some(ctor_def_id) = variant.data.ctor_def_id() {
531 struct_constructors.insert(ctor_def_id, variant.def_id);
537 let of_trait = tcx.impl_trait_ref(id.owner_id);
539 if of_trait.is_some() {
540 worklist.push(id.owner_id.def_id);
543 // get DefIds from another query
544 let local_def_ids = tcx
545 .associated_item_def_ids(id.owner_id)
547 .filter_map(|def_id| def_id.as_local());
549 // And we access the Map here to get HirId from LocalDefId
550 for id in local_def_ids {
551 if of_trait.is_some()
552 || has_allow_dead_code_or_lang_attr(tcx, tcx.hir().local_def_id_to_hir_id(id))
559 let item = tcx.hir().item(id);
560 if let hir::ItemKind::Struct(ref variant_data, _) = item.kind
561 && let Some(ctor_hir_id) = variant_data.ctor_hir_id()
563 struct_constructors.insert(tcx.hir().local_def_id(ctor_hir_id), item.owner_id.def_id);
566 DefKind::GlobalAsm => {
567 // global_asm! is always live.
568 worklist.push(id.owner_id.def_id);
574 fn check_trait_item(tcx: TyCtxt<'_>, worklist: &mut Vec<LocalDefId>, id: hir::TraitItemId) {
575 use hir::TraitItemKind::{Const, Fn};
576 if matches!(tcx.def_kind(id.owner_id), DefKind::AssocConst | DefKind::AssocFn) {
577 let trait_item = tcx.hir().trait_item(id);
578 if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_)))
579 && has_allow_dead_code_or_lang_attr(tcx, trait_item.hir_id())
581 worklist.push(trait_item.owner_id.def_id);
586 fn check_foreign_item(tcx: TyCtxt<'_>, worklist: &mut Vec<LocalDefId>, id: hir::ForeignItemId) {
587 if matches!(tcx.def_kind(id.owner_id), DefKind::Static(_) | DefKind::Fn)
588 && has_allow_dead_code_or_lang_attr(tcx, id.hir_id())
590 worklist.push(id.owner_id.def_id);
594 fn create_and_seed_worklist(
596 ) -> (Vec<LocalDefId>, FxHashMap<LocalDefId, LocalDefId>) {
597 let effective_visibilities = &tcx.effective_visibilities(());
598 // see `MarkSymbolVisitor::struct_constructors`
599 let mut struct_constructors = Default::default();
600 let mut worklist = effective_visibilities
602 .filter_map(|(&id, effective_vis)| {
603 effective_vis.is_public_at_level(Level::Reachable).then_some(id)
606 .chain(tcx.entry_fn(()).and_then(|(def_id, _)| def_id.as_local()))
607 .collect::<Vec<_>>();
609 let crate_items = tcx.hir_crate_items(());
610 for id in crate_items.items() {
611 check_item(tcx, &mut worklist, &mut struct_constructors, id);
614 for id in crate_items.trait_items() {
615 check_trait_item(tcx, &mut worklist, id);
618 for id in crate_items.foreign_items() {
619 check_foreign_item(tcx, &mut worklist, id);
622 (worklist, struct_constructors)
625 fn live_symbols_and_ignored_derived_traits(
628 ) -> (FxHashSet<LocalDefId>, FxHashMap<LocalDefId, Vec<(DefId, DefId)>>) {
629 let (worklist, struct_constructors) = create_and_seed_worklist(tcx);
630 let mut symbol_visitor = MarkSymbolVisitor {
633 maybe_typeck_results: None,
634 live_symbols: Default::default(),
635 repr_has_repr_c: false,
636 repr_has_repr_simd: false,
638 ignore_variant_stack: vec![],
640 ignored_derived_traits: FxHashMap::default(),
642 symbol_visitor.mark_live_symbols();
643 (symbol_visitor.live_symbols, symbol_visitor.ignored_derived_traits)
652 struct DeadVisitor<'tcx> {
654 live_symbols: &'tcx FxHashSet<LocalDefId>,
655 ignored_derived_traits: &'tcx FxHashMap<LocalDefId, Vec<(DefId, DefId)>>,
658 enum ShouldWarnAboutField {
659 Yes(bool), // positional?
663 impl<'tcx> DeadVisitor<'tcx> {
664 fn should_warn_about_field(&mut self, field: &ty::FieldDef) -> ShouldWarnAboutField {
665 if self.live_symbols.contains(&field.did.expect_local()) {
666 return ShouldWarnAboutField::No;
668 let field_type = self.tcx.type_of(field.did);
669 if field_type.is_phantom_data() {
670 return ShouldWarnAboutField::No;
672 let is_positional = field.name.as_str().starts_with(|c: char| c.is_ascii_digit());
676 .layout_of(self.tcx.param_env(field.did).and(field_type))
677 .map_or(true, |layout| layout.is_zst())
679 return ShouldWarnAboutField::No;
681 ShouldWarnAboutField::Yes(is_positional)
684 fn warn_multiple_dead_codes(
686 dead_codes: &[LocalDefId],
688 parent_item: Option<LocalDefId>,
691 let Some(&first_id) = dead_codes.first() else {
696 dead_codes.iter().map(|&def_id| tcx.item_name(def_id.to_def_id())).collect();
697 let spans: Vec<_> = dead_codes
699 .map(|&def_id| match tcx.def_ident_span(def_id) {
700 Some(s) => s.with_ctxt(tcx.def_span(def_id).ctxt()),
701 None => tcx.def_span(def_id),
705 let descr = tcx.def_kind(first_id).descr(first_id.to_def_id());
706 let num = dead_codes.len();
707 let multiple = num > 6;
708 let name_list = names.into();
710 let lint = if is_positional {
711 lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS
713 lint::builtin::DEAD_CODE
716 let parent_info = if let Some(parent_item) = parent_item {
717 let parent_descr = tcx.def_kind(parent_item).descr(parent_item.to_def_id());
722 span: tcx.def_ident_span(parent_item).unwrap(),
728 let encl_def_id = parent_item.unwrap_or(first_id);
729 let ignored_derived_impls =
730 if let Some(ign_traits) = self.ignored_derived_traits.get(&encl_def_id) {
731 let trait_list = ign_traits
733 .map(|(trait_id, _)| self.tcx.item_name(*trait_id))
734 .collect::<Vec<_>>();
735 let trait_list_len = trait_list.len();
736 Some(IgnoredDerivedImpls {
737 name: self.tcx.item_name(encl_def_id.to_def_id()),
738 trait_list: trait_list.into(),
745 let diag = if is_positional {
746 MultipleDeadCodes::UnusedTupleStructFields {
752 change_fields_suggestion: ChangeFieldsToBeOfUnitType { num, spans: spans.clone() },
754 ignored_derived_impls,
757 MultipleDeadCodes::DeadCodes {
764 ignored_derived_impls,
768 self.tcx.emit_spanned_lint(
770 tcx.hir().local_def_id_to_hir_id(first_id),
771 MultiSpan::from_spans(spans),
776 fn warn_dead_fields_and_variants(
780 dead_codes: Vec<DeadVariant>,
783 let mut dead_codes = dead_codes
785 .filter(|v| !v.name.as_str().starts_with('_'))
786 .collect::<Vec<&DeadVariant>>();
787 if dead_codes.is_empty() {
790 dead_codes.sort_by_key(|v| v.level);
791 for (_, group) in &dead_codes.into_iter().group_by(|v| v.level) {
792 self.warn_multiple_dead_codes(
793 &group.map(|v| v.def_id).collect::<Vec<_>>(),
801 fn warn_dead_code(&mut self, id: LocalDefId, participle: &str) {
802 self.warn_multiple_dead_codes(&[id], participle, None, false);
805 fn check_definition(&mut self, def_id: LocalDefId) {
806 if self.live_symbols.contains(&def_id) {
809 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
810 if has_allow_dead_code_or_lang_attr(self.tcx, hir_id) {
813 let Some(name) = self.tcx.opt_item_name(def_id.to_def_id()) else {
816 if name.as_str().starts_with('_') {
819 match self.tcx.def_kind(def_id) {
828 | DefKind::ForeignTy => self.warn_dead_code(def_id, "used"),
829 DefKind::Struct => self.warn_dead_code(def_id, "constructed"),
830 DefKind::Variant | DefKind::Field => bug!("should be handled specially"),
836 fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalDefId) {
837 let (live_symbols, ignored_derived_traits) = tcx.live_symbols_and_ignored_derived_traits(());
838 let mut visitor = DeadVisitor { tcx, live_symbols, ignored_derived_traits };
840 let module_items = tcx.hir_module_items(module);
842 for item in module_items.items() {
843 if !live_symbols.contains(&item.owner_id.def_id) {
844 let parent = tcx.local_parent(item.owner_id.def_id);
845 if parent != module && !live_symbols.contains(&parent) {
846 // We already have diagnosed something.
849 visitor.check_definition(item.owner_id.def_id);
853 let def_kind = tcx.def_kind(item.owner_id);
854 if let DefKind::Struct | DefKind::Union | DefKind::Enum = def_kind {
855 let adt = tcx.adt_def(item.owner_id);
856 let mut dead_variants = Vec::new();
858 for variant in adt.variants() {
859 let def_id = variant.def_id.expect_local();
860 if !live_symbols.contains(&def_id) {
861 // Record to group diagnostics.
862 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
863 let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
864 dead_variants.push(DeadVariant { def_id, name: variant.name, level });
868 let mut is_positional = false;
869 let dead_fields = variant
872 .filter_map(|field| {
873 let def_id = field.did.expect_local();
874 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
875 if let ShouldWarnAboutField::Yes(is_pos) =
876 visitor.should_warn_about_field(&field)
881 is_positional = true;
882 lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS
884 lint::builtin::DEAD_CODE
889 Some(DeadVariant { def_id, name: field.name, level })
895 visitor.warn_dead_fields_and_variants(def_id, "read", dead_fields, is_positional)
898 visitor.warn_dead_fields_and_variants(
899 item.owner_id.def_id,
907 for impl_item in module_items.impl_items() {
908 visitor.check_definition(impl_item.owner_id.def_id);
911 for foreign_item in module_items.foreign_items() {
912 visitor.check_definition(foreign_item.owner_id.def_id);
915 // We do not warn trait items.
918 pub(crate) fn provide(providers: &mut Providers) {
920 Providers { live_symbols_and_ignored_derived_traits, check_mod_deathness, ..*providers };