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-rw-r--r--compiler/rustc_passes/src/dead.rs467
1 files changed, 196 insertions, 271 deletions
diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index a90d1af87ca..fa9d0c7b1b7 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -5,7 +5,6 @@
 
 use std::mem;
 
-use hir::ItemKind;
 use hir::def_id::{LocalDefIdMap, LocalDefIdSet};
 use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::FxIndexSet;
@@ -14,7 +13,7 @@ use rustc_errors::MultiSpan;
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
 use rustc_hir::intravisit::{self, Visitor};
-use rustc_hir::{self as hir, ImplItem, ImplItemKind, Node, PatKind, QPath, TyKind};
+use rustc_hir::{self as hir, Node, PatKind, QPath};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::privacy::Level;
 use rustc_middle::query::Providers;
@@ -28,37 +27,43 @@ use crate::errors::{
     ChangeFields, IgnoredDerivedImpls, MultipleDeadCodes, ParentInfo, UselessAssignment,
 };
 
-// Any local node that may call something in its body block should be
-// explored. For example, if it's a live Node::Item that is a
-// function, then we should explore its block to check for codes that
-// may need to be marked as live.
+/// Any local definition that may call something in its body block should be explored. For example,
+/// if it's a live 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_node_by_def_id(def_id),
-        Node::Item(..)
-            | Node::ImplItem(..)
-            | Node::ForeignItem(..)
-            | Node::TraitItem(..)
-            | Node::Variant(..)
-            | Node::AnonConst(..)
-            | Node::OpaqueTy(..)
-    )
-}
-
-/// Returns the local def id of the ADT if the given ty refers to a local one.
-fn local_adt_def_of_ty<'tcx>(ty: &hir::Ty<'tcx>) -> Option<LocalDefId> {
-    match ty.kind {
-        TyKind::Path(QPath::Resolved(_, path)) => {
-            if let Res::Def(def_kind, def_id) = path.res
-                && let Some(local_def_id) = def_id.as_local()
-                && matches!(def_kind, DefKind::Struct | DefKind::Enum | DefKind::Union)
-            {
-                Some(local_def_id)
-            } else {
-                None
-            }
-        }
-        _ => None,
+    match tcx.def_kind(def_id) {
+        DefKind::Mod
+        | DefKind::Struct
+        | DefKind::Union
+        | DefKind::Enum
+        | DefKind::Variant
+        | DefKind::Trait
+        | DefKind::TyAlias
+        | DefKind::ForeignTy
+        | DefKind::TraitAlias
+        | DefKind::AssocTy
+        | DefKind::Fn
+        | DefKind::Const
+        | DefKind::Static { .. }
+        | DefKind::AssocFn
+        | DefKind::AssocConst
+        | DefKind::Macro(_)
+        | DefKind::GlobalAsm
+        | DefKind::Impl { .. }
+        | DefKind::OpaqueTy
+        | DefKind::AnonConst
+        | DefKind::InlineConst
+        | DefKind::ExternCrate
+        | DefKind::Use
+        | DefKind::Ctor(..)
+        | DefKind::ForeignMod => true,
+
+        DefKind::TyParam
+        | DefKind::ConstParam
+        | DefKind::Field
+        | DefKind::LifetimeParam
+        | DefKind::Closure
+        | DefKind::SyntheticCoroutineBody => false,
     }
 }
 
@@ -74,17 +79,16 @@ struct MarkSymbolVisitor<'tcx> {
     worklist: Vec<(LocalDefId, ComesFromAllowExpect)>,
     tcx: TyCtxt<'tcx>,
     maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
+    scanned: UnordSet<(LocalDefId, ComesFromAllowExpect)>,
     live_symbols: LocalDefIdSet,
     repr_unconditionally_treats_fields_as_live: 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: LocalDefIdMap<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: LocalDefIdMap<FxIndexSet<(DefId, DefId)>>,
+    ignored_derived_traits: LocalDefIdMap<FxIndexSet<DefId>>,
 }
 
 impl<'tcx> MarkSymbolVisitor<'tcx> {
@@ -99,7 +103,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
 
     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) {
+            if should_explore(self.tcx, def_id) {
                 self.worklist.push((def_id, ComesFromAllowExpect::No));
             }
             self.live_symbols.insert(def_id);
@@ -318,13 +322,12 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
     }
 
     fn mark_live_symbols(&mut self) {
-        let mut scanned = UnordSet::default();
         while let Some(work) = self.worklist.pop() {
-            if !scanned.insert(work) {
+            if !self.scanned.insert(work) {
                 continue;
             }
 
-            let (id, comes_from_allow_expect) = work;
+            let (mut id, comes_from_allow_expect) = work;
 
             // Avoid accessing the HIR for the synthesized associated type generated for RPITITs.
             if self.tcx.is_impl_trait_in_trait(id.to_def_id()) {
@@ -332,9 +335,11 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                 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);
+            // in the case of tuple struct constructors we want to check the item,
+            // not the generated tuple struct constructor function
+            if let DefKind::Ctor(..) = self.tcx.def_kind(id) {
+                id = self.tcx.local_parent(id);
+            }
 
             // When using `#[allow]` or `#[expect]` of `dead_code`, we do a QOL improvement
             // by declaring fn calls, statics, ... within said items as live, as well as
@@ -380,10 +385,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                 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()
-                        .insert((trait_of, impl_of));
+                    self.ignored_derived_traits.entry(adt_def_id).or_default().insert(trait_of);
                 }
                 return true;
             }
@@ -478,24 +480,24 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
     /// `local_def_id` points to an impl or an impl item,
     /// both impl and impl item that may be passed to this function are of a trait,
     /// and added into the unsolved_items during `create_and_seed_worklist`
-    fn check_impl_or_impl_item_live(
-        &mut self,
-        impl_id: hir::ItemId,
-        local_def_id: LocalDefId,
-    ) -> bool {
-        let trait_def_id = match self.tcx.def_kind(local_def_id) {
+    fn check_impl_or_impl_item_live(&mut self, local_def_id: LocalDefId) -> bool {
+        let (impl_block_id, trait_def_id) = match self.tcx.def_kind(local_def_id) {
             // assoc impl items of traits are live if the corresponding trait items are live
-            DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn => self
-                .tcx
-                .associated_item(local_def_id)
-                .trait_item_def_id
-                .and_then(|def_id| def_id.as_local()),
+            DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn => (
+                self.tcx.local_parent(local_def_id),
+                self.tcx
+                    .associated_item(local_def_id)
+                    .trait_item_def_id
+                    .and_then(|def_id| def_id.as_local()),
+            ),
             // impl items are live if the corresponding traits are live
-            DefKind::Impl { of_trait: true } => self
-                .tcx
-                .impl_trait_ref(impl_id.owner_id.def_id)
-                .and_then(|trait_ref| trait_ref.skip_binder().def_id.as_local()),
-            _ => None,
+            DefKind::Impl { of_trait: true } => (
+                local_def_id,
+                self.tcx
+                    .impl_trait_ref(local_def_id)
+                    .and_then(|trait_ref| trait_ref.skip_binder().def_id.as_local()),
+            ),
+            _ => bug!(),
         };
 
         if let Some(trait_def_id) = trait_def_id
@@ -505,9 +507,9 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
         }
 
         // The impl or impl item is used if the corresponding trait or trait item is used and the ty is used.
-        if let Some(local_def_id) =
-            local_adt_def_of_ty(self.tcx.hir_item(impl_id).expect_impl().self_ty)
-            && !self.live_symbols.contains(&local_def_id)
+        if let ty::Adt(adt, _) = self.tcx.type_of(impl_block_id).instantiate_identity().kind()
+            && let Some(adt_def_id) = adt.did().as_local()
+            && !self.live_symbols.contains(&adt_def_id)
         {
             return false;
         }
@@ -714,139 +716,86 @@ fn has_allow_dead_code_or_lang_attr(
     }
 }
 
-// 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>(
+/// Examine the given definition and record it in the worklist if it should be considered live.
+///
+/// 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=".."]
+///       Lang items are always callable from elsewhere.
+///
+/// For trait methods and implementations of traits, we are not certain that the definitions are
+/// live at this stage. We record them in `unsolved_items` for later examination.
+fn maybe_record_as_seed<'tcx>(
     tcx: TyCtxt<'tcx>,
+    owner_id: hir::OwnerId,
     worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>,
-    struct_constructors: &mut LocalDefIdMap<LocalDefId>,
-    unsolved_items: &mut Vec<(hir::ItemId, LocalDefId)>,
-    id: hir::ItemId,
+    unsolved_items: &mut Vec<LocalDefId>,
 ) {
-    let allow_dead_code = has_allow_dead_code_or_lang_attr(tcx, id.owner_id.def_id);
+    let allow_dead_code = has_allow_dead_code_or_lang_attr(tcx, owner_id.def_id);
     if let Some(comes_from_allow) = allow_dead_code {
-        worklist.push((id.owner_id.def_id, comes_from_allow));
+        worklist.push((owner_id.def_id, comes_from_allow));
     }
 
-    match tcx.def_kind(id.owner_id) {
+    match tcx.def_kind(owner_id) {
         DefKind::Enum => {
-            let item = tcx.hir_item(id);
-            if let hir::ItemKind::Enum(_, _, ref enum_def) = item.kind {
-                if let Some(comes_from_allow) = allow_dead_code {
-                    worklist.extend(
-                        enum_def.variants.iter().map(|variant| (variant.def_id, comes_from_allow)),
-                    );
-                }
-
-                for variant in enum_def.variants {
-                    if let Some(ctor_def_id) = variant.data.ctor_def_id() {
-                        struct_constructors.insert(ctor_def_id, variant.def_id);
-                    }
-                }
+            if let Some(comes_from_allow) = allow_dead_code {
+                let adt = tcx.adt_def(owner_id);
+                worklist.extend(
+                    adt.variants()
+                        .iter()
+                        .map(|variant| (variant.def_id.expect_local(), comes_from_allow)),
+                );
             }
         }
-        DefKind::Impl { of_trait } => {
-            if let Some(comes_from_allow) =
-                has_allow_dead_code_or_lang_attr(tcx, id.owner_id.def_id)
-            {
-                worklist.push((id.owner_id.def_id, comes_from_allow));
-            } else if of_trait {
-                unsolved_items.push((id, id.owner_id.def_id));
-            }
-
-            for def_id in tcx.associated_item_def_ids(id.owner_id) {
-                let local_def_id = def_id.expect_local();
-
-                if let Some(comes_from_allow) = has_allow_dead_code_or_lang_attr(tcx, local_def_id)
-                {
-                    worklist.push((local_def_id, comes_from_allow));
-                } else if of_trait {
-                    // We only care about associated items of traits,
-                    // because they cannot be visited directly,
-                    // so we later mark them as live if their corresponding traits
-                    // or trait items and self types are both live,
-                    // but inherent associated items can be visited and marked directly.
-                    unsolved_items.push((id, local_def_id));
+        DefKind::AssocFn | DefKind::AssocConst | DefKind::AssocTy => {
+            if allow_dead_code.is_none() {
+                let parent = tcx.local_parent(owner_id.def_id);
+                match tcx.def_kind(parent) {
+                    DefKind::Impl { of_trait: false } | DefKind::Trait => {}
+                    DefKind::Impl { of_trait: true } => {
+                        // We only care about associated items of traits,
+                        // because they cannot be visited directly,
+                        // so we later mark them as live if their corresponding traits
+                        // or trait items and self types are both live,
+                        // but inherent associated items can be visited and marked directly.
+                        unsolved_items.push(owner_id.def_id);
+                    }
+                    _ => bug!(),
                 }
             }
         }
-        DefKind::Struct => {
-            let item = tcx.hir_item(id);
-            if let hir::ItemKind::Struct(_, _, ref variant_data) = item.kind
-                && let Some(ctor_def_id) = variant_data.ctor_def_id()
-            {
-                struct_constructors.insert(ctor_def_id, item.owner_id.def_id);
+        DefKind::Impl { of_trait: true } => {
+            if allow_dead_code.is_none() {
+                unsolved_items.push(owner_id.def_id);
             }
         }
         DefKind::GlobalAsm => {
             // global_asm! is always live.
-            worklist.push((id.owner_id.def_id, ComesFromAllowExpect::No));
+            worklist.push((owner_id.def_id, ComesFromAllowExpect::No));
         }
         DefKind::Const => {
-            let item = tcx.hir_item(id);
-            if let hir::ItemKind::Const(ident, ..) = item.kind
-                && ident.name == kw::Underscore
-            {
+            if tcx.item_name(owner_id.def_id) == kw::Underscore {
                 // `const _` is always live, as that syntax only exists for the side effects
                 // of type checking and evaluating the constant expression, and marking them
                 // as dead code would defeat that purpose.
-                worklist.push((id.owner_id.def_id, ComesFromAllowExpect::No));
+                worklist.push((owner_id.def_id, ComesFromAllowExpect::No));
             }
         }
         _ => {}
     }
 }
 
-fn check_trait_item(
-    tcx: TyCtxt<'_>,
-    worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>,
-    id: hir::TraitItemId,
-) {
-    use hir::TraitItemKind::{Const, Fn, Type};
-
-    let trait_item = tcx.hir_trait_item(id);
-    if matches!(trait_item.kind, Const(_, Some(_)) | Type(_, Some(_)) | Fn(..))
-        && let Some(comes_from_allow) =
-            has_allow_dead_code_or_lang_attr(tcx, trait_item.owner_id.def_id)
-    {
-        worklist.push((trait_item.owner_id.def_id, comes_from_allow));
-    }
-}
-
-fn check_foreign_item(
-    tcx: TyCtxt<'_>,
-    worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>,
-    id: hir::ForeignItemId,
-) {
-    if matches!(tcx.def_kind(id.owner_id), DefKind::Static { .. } | DefKind::Fn)
-        && let Some(comes_from_allow) = has_allow_dead_code_or_lang_attr(tcx, id.owner_id.def_id)
-    {
-        worklist.push((id.owner_id.def_id, comes_from_allow));
-    }
-}
-
 fn create_and_seed_worklist(
     tcx: TyCtxt<'_>,
-) -> (
-    Vec<(LocalDefId, ComesFromAllowExpect)>,
-    LocalDefIdMap<LocalDefId>,
-    Vec<(hir::ItemId, LocalDefId)>,
-) {
+) -> (Vec<(LocalDefId, ComesFromAllowExpect)>, Vec<LocalDefId>) {
     let effective_visibilities = &tcx.effective_visibilities(());
-    // see `MarkSymbolVisitor::struct_constructors`
     let mut unsolved_impl_item = Vec::new();
-    let mut struct_constructors = Default::default();
     let mut worklist = effective_visibilities
         .iter()
         .filter_map(|(&id, effective_vis)| {
@@ -863,54 +812,49 @@ fn create_and_seed_worklist(
         .collect::<Vec<_>>();
 
     let crate_items = tcx.hir_crate_items(());
-    for id in crate_items.free_items() {
-        check_item(tcx, &mut worklist, &mut struct_constructors, &mut unsolved_impl_item, 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);
+    for id in crate_items.owners() {
+        maybe_record_as_seed(tcx, id, &mut worklist, &mut unsolved_impl_item);
     }
 
-    (worklist, struct_constructors, unsolved_impl_item)
+    (worklist, unsolved_impl_item)
 }
 
 fn live_symbols_and_ignored_derived_traits(
     tcx: TyCtxt<'_>,
     (): (),
-) -> (LocalDefIdSet, LocalDefIdMap<FxIndexSet<(DefId, DefId)>>) {
-    let (worklist, struct_constructors, mut unsolved_items) = create_and_seed_worklist(tcx);
+) -> (LocalDefIdSet, LocalDefIdMap<FxIndexSet<DefId>>) {
+    let (worklist, mut unsolved_items) = create_and_seed_worklist(tcx);
     let mut symbol_visitor = MarkSymbolVisitor {
         worklist,
         tcx,
         maybe_typeck_results: None,
+        scanned: Default::default(),
         live_symbols: Default::default(),
         repr_unconditionally_treats_fields_as_live: false,
         repr_has_repr_simd: false,
         in_pat: false,
         ignore_variant_stack: vec![],
-        struct_constructors,
         ignored_derived_traits: Default::default(),
     };
     symbol_visitor.mark_live_symbols();
-    let mut items_to_check;
-    (items_to_check, unsolved_items) =
-        unsolved_items.into_iter().partition(|&(impl_id, local_def_id)| {
-            symbol_visitor.check_impl_or_impl_item_live(impl_id, local_def_id)
-        });
+
+    // We have marked the primary seeds as live. We now need to process unsolved items from traits
+    // and trait impls: add them to the work list if the trait or the implemented type is live.
+    let mut items_to_check: Vec<_> = unsolved_items
+        .extract_if(.., |&mut local_def_id| {
+            symbol_visitor.check_impl_or_impl_item_live(local_def_id)
+        })
+        .collect();
 
     while !items_to_check.is_empty() {
-        symbol_visitor.worklist =
-            items_to_check.into_iter().map(|(_, id)| (id, ComesFromAllowExpect::No)).collect();
+        symbol_visitor
+            .worklist
+            .extend(items_to_check.drain(..).map(|id| (id, ComesFromAllowExpect::No)));
         symbol_visitor.mark_live_symbols();
 
-        (items_to_check, unsolved_items) =
-            unsolved_items.into_iter().partition(|&(impl_id, local_def_id)| {
-                symbol_visitor.check_impl_or_impl_item_live(impl_id, local_def_id)
-            });
+        items_to_check.extend(unsolved_items.extract_if(.., |&mut local_def_id| {
+            symbol_visitor.check_impl_or_impl_item_live(local_def_id)
+        }));
     }
 
     (symbol_visitor.live_symbols, symbol_visitor.ignored_derived_traits)
@@ -925,7 +869,7 @@ struct DeadItem {
 struct DeadVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
     live_symbols: &'tcx LocalDefIdSet,
-    ignored_derived_traits: &'tcx LocalDefIdMap<FxIndexSet<(DefId, DefId)>>,
+    ignored_derived_traits: &'tcx LocalDefIdMap<FxIndexSet<DefId>>,
 }
 
 enum ShouldWarnAboutField {
@@ -984,25 +928,7 @@ impl<'tcx> DeadVisitor<'tcx> {
         parent_item: Option<LocalDefId>,
         report_on: ReportOn,
     ) {
-        fn get_parent_if_enum_variant<'tcx>(
-            tcx: TyCtxt<'tcx>,
-            may_variant: LocalDefId,
-        ) -> LocalDefId {
-            if let Node::Variant(_) = tcx.hir_node_by_def_id(may_variant)
-                && let Some(enum_did) = tcx.opt_parent(may_variant.to_def_id())
-                && let Some(enum_local_id) = enum_did.as_local()
-                && let Node::Item(item) = tcx.hir_node_by_def_id(enum_local_id)
-                && let ItemKind::Enum(..) = item.kind
-            {
-                enum_local_id
-            } else {
-                may_variant
-            }
-        }
-
-        let Some(&first_item) = dead_codes.first() else {
-            return;
-        };
+        let Some(&first_item) = dead_codes.first() else { return };
         let tcx = self.tcx;
 
         let first_lint_level = first_item.level;
@@ -1011,81 +937,54 @@ impl<'tcx> DeadVisitor<'tcx> {
         let names: Vec<_> = dead_codes.iter().map(|item| item.name).collect();
         let spans: Vec<_> = dead_codes
             .iter()
-            .map(|item| match tcx.def_ident_span(item.def_id) {
-                Some(s) => s.with_ctxt(tcx.def_span(item.def_id).ctxt()),
-                None => tcx.def_span(item.def_id),
+            .map(|item| {
+                let span = tcx.def_span(item.def_id);
+                let ident_span = tcx.def_ident_span(item.def_id);
+                // FIXME(cjgillot) this SyntaxContext manipulation does not make any sense.
+                ident_span.map(|s| s.with_ctxt(span.ctxt())).unwrap_or(span)
             })
             .collect();
 
-        let descr = tcx.def_descr(first_item.def_id.to_def_id());
+        let mut descr = tcx.def_descr(first_item.def_id.to_def_id());
         // `impl` blocks are "batched" and (unlike other batching) might
         // contain different kinds of associated items.
-        let descr = if dead_codes.iter().any(|item| tcx.def_descr(item.def_id.to_def_id()) != descr)
-        {
-            "associated item"
-        } else {
-            descr
-        };
+        if dead_codes.iter().any(|item| tcx.def_descr(item.def_id.to_def_id()) != descr) {
+            descr = "associated item"
+        }
+
         let num = dead_codes.len();
         let multiple = num > 6;
         let name_list = names.into();
 
-        let parent_info = if let Some(parent_item) = parent_item {
+        let parent_info = parent_item.map(|parent_item| {
             let parent_descr = tcx.def_descr(parent_item.to_def_id());
             let span = if let DefKind::Impl { .. } = tcx.def_kind(parent_item) {
                 tcx.def_span(parent_item)
             } else {
                 tcx.def_ident_span(parent_item).unwrap()
             };
-            Some(ParentInfo { num, descr, parent_descr, span })
-        } else {
-            None
-        };
+            ParentInfo { num, descr, parent_descr, span }
+        });
 
-        let encl_def_id = parent_item.unwrap_or(first_item.def_id);
-        // If parent of encl_def_id is an enum, use the parent ID instead.
-        let encl_def_id = get_parent_if_enum_variant(tcx, encl_def_id);
+        let mut encl_def_id = parent_item.unwrap_or(first_item.def_id);
+        // `ignored_derived_traits` is computed for the enum, not for the variants.
+        if let DefKind::Variant = tcx.def_kind(encl_def_id) {
+            encl_def_id = tcx.local_parent(encl_def_id);
+        }
 
         let ignored_derived_impls =
-            if let Some(ign_traits) = self.ignored_derived_traits.get(&encl_def_id) {
+            self.ignored_derived_traits.get(&encl_def_id).map(|ign_traits| {
                 let trait_list = ign_traits
                     .iter()
-                    .map(|(trait_id, _)| self.tcx.item_name(*trait_id))
+                    .map(|trait_id| self.tcx.item_name(*trait_id))
                     .collect::<Vec<_>>();
                 let trait_list_len = trait_list.len();
-                Some(IgnoredDerivedImpls {
+                IgnoredDerivedImpls {
                     name: self.tcx.item_name(encl_def_id.to_def_id()),
                     trait_list: trait_list.into(),
                     trait_list_len,
-                })
-            } else {
-                None
-            };
-
-        let enum_variants_with_same_name = dead_codes
-            .iter()
-            .filter_map(|dead_item| {
-                if let Node::ImplItem(ImplItem {
-                    kind: ImplItemKind::Fn(..) | ImplItemKind::Const(..),
-                    ..
-                }) = tcx.hir_node_by_def_id(dead_item.def_id)
-                    && let Some(impl_did) = tcx.opt_parent(dead_item.def_id.to_def_id())
-                    && let DefKind::Impl { of_trait: false } = tcx.def_kind(impl_did)
-                    && let ty::Adt(maybe_enum, _) = tcx.type_of(impl_did).skip_binder().kind()
-                    && maybe_enum.is_enum()
-                    && let Some(variant) =
-                        maybe_enum.variants().iter().find(|i| i.name == dead_item.name)
-                {
-                    Some(crate::errors::EnumVariantSameName {
-                        dead_descr: tcx.def_descr(dead_item.def_id.to_def_id()),
-                        dead_name: dead_item.name,
-                        variant_span: tcx.def_span(variant.def_id),
-                    })
-                } else {
-                    None
                 }
-            })
-            .collect();
+            });
 
         let diag = match report_on {
             ReportOn::TupleField => {
@@ -1132,16 +1031,42 @@ impl<'tcx> DeadVisitor<'tcx> {
                     ignored_derived_impls,
                 }
             }
-            ReportOn::NamedField => MultipleDeadCodes::DeadCodes {
-                multiple,
-                num,
-                descr,
-                participle,
-                name_list,
-                parent_info,
-                ignored_derived_impls,
-                enum_variants_with_same_name,
-            },
+            ReportOn::NamedField => {
+                let enum_variants_with_same_name = dead_codes
+                    .iter()
+                    .filter_map(|dead_item| {
+                        if let DefKind::AssocFn | DefKind::AssocConst =
+                            tcx.def_kind(dead_item.def_id)
+                            && let impl_did = tcx.local_parent(dead_item.def_id)
+                            && let DefKind::Impl { of_trait: false } = tcx.def_kind(impl_did)
+                            && let ty::Adt(maybe_enum, _) =
+                                tcx.type_of(impl_did).instantiate_identity().kind()
+                            && maybe_enum.is_enum()
+                            && let Some(variant) =
+                                maybe_enum.variants().iter().find(|i| i.name == dead_item.name)
+                        {
+                            Some(crate::errors::EnumVariantSameName {
+                                dead_descr: tcx.def_descr(dead_item.def_id.to_def_id()),
+                                dead_name: dead_item.name,
+                                variant_span: tcx.def_span(variant.def_id),
+                            })
+                        } else {
+                            None
+                        }
+                    })
+                    .collect();
+
+                MultipleDeadCodes::DeadCodes {
+                    multiple,
+                    num,
+                    descr,
+                    participle,
+                    name_list,
+                    parent_info,
+                    ignored_derived_impls,
+                    enum_variants_with_same_name,
+                }
+            }
         };
 
         let hir_id = tcx.local_def_id_to_hir_id(first_item.def_id);