diff options
Diffstat (limited to 'compiler/rustc_passes/src/dead.rs')
| -rw-r--r-- | compiler/rustc_passes/src/dead.rs | 960 |
1 files changed, 960 insertions, 0 deletions
diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs new file mode 100644 index 000000000..1e2fbeb38 --- /dev/null +++ b/compiler/rustc_passes/src/dead.rs @@ -0,0 +1,960 @@ +// 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 }; +} |