Revert "Rollup merge of #127017 - mu001999-contrib:dead/enhance, r=pnkfelix"

This reverts commit a70dc297a899b76793a14c5705f6ec78fd7a57a7, reversing
changes made to ceae37188b9f1be527bb16c9d657a161be7dbbe3.

3 files changed, 10 insertions, 87 deletions

diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index 3b1a796130c..9c475c9fbf4 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -55,24 +55,7 @@ impl Publicness {
     }
 }
 
-fn adt_of<'tcx>(ty: &hir::Ty<'tcx>) -> Option<(LocalDefId, DefKind)> {
-    match ty.kind {
-        TyKind::Path(hir::QPath::Resolved(_, path)) => {
-            if let Res::Def(def_kind, def_id) = path.res
-                && let Some(local_def_id) = def_id.as_local()
-            {
-                Some((local_def_id, def_kind))
-            } else {
-                None
-            }
-        }
-        TyKind::Slice(ty) | TyKind::Array(ty, _) => adt_of(ty),
-        TyKind::Ptr(ty) | TyKind::Ref(_, ty) => adt_of(ty.ty),
-        _ => None,
-    }
-}
-
-fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: LocalDefId) -> bool {
+fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> bool {
     // treat PhantomData and positional ZST as public,
     // we don't want to lint types which only have them,
     // cause it's a common way to use such types to check things like well-formedness
@@ -97,7 +80,10 @@ fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: LocalDefId) -> bool {
 /// for enum and union, just check they are public,
 /// and doesn't solve types like &T for now, just skip them
 fn ty_ref_to_pub_struct(tcx: TyCtxt<'_>, ty: &hir::Ty<'_>) -> Publicness {
-    if let Some((def_id, def_kind)) = adt_of(ty) {
+    if let TyKind::Path(hir::QPath::Resolved(_, path)) = ty.kind
+        && let Res::Def(def_kind, def_id) = path.res
+        && def_id.is_local()
+    {
         return match def_kind {
             DefKind::Enum | DefKind::Union => {
                 let ty_is_public = tcx.visibility(def_id).is_public();
@@ -580,8 +566,10 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
     }
 
     fn impl_item_with_used_self(&mut self, impl_id: hir::ItemId, impl_item_id: LocalDefId) -> bool {
-        if let Some((local_def_id, def_kind)) =
-            adt_of(self.tcx.hir().item(impl_id).expect_impl().self_ty)
+        if let TyKind::Path(hir::QPath::Resolved(_, path)) =
+            self.tcx.hir().item(impl_id).expect_impl().self_ty.kind
+            && 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)
         {
             if let Some(trait_item_id) = self.tcx.associated_item(impl_item_id).trait_item_def_id
@@ -928,7 +916,7 @@ fn create_and_seed_worklist(
                     match tcx.def_kind(id) {
                         DefKind::Impl { .. } => false,
                         DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn => !matches!(tcx.associated_item(id).container, AssocItemContainer::ImplContainer),
-                        DefKind::Struct => struct_all_fields_are_public(tcx, id) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
+                        DefKind::Struct => struct_all_fields_are_public(tcx, id.to_def_id()) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
                         _ => true
                     })
                 .map(|id| (id, ComesFromAllowExpect::No))
diff --git a/tests/ui/lint/dead-code/unused-impl-for-non-adts.rs b/tests/ui/lint/dead-code/unused-impl-for-non-adts.rs
deleted file mode 100644
index 46065dcee81..00000000000
--- a/tests/ui/lint/dead-code/unused-impl-for-non-adts.rs
+++ /dev/null
@@ -1,45 +0,0 @@
-#![deny(dead_code)]
-
-struct Foo; //~ ERROR struct `Foo` is never constructed
-
-trait Trait { //~ ERROR trait `Trait` is never used
-    fn foo(&self) {}
-}
-
-impl Trait for Foo {}
-
-impl Trait for [Foo] {}
-impl<const N: usize> Trait for [Foo; N] {}
-
-impl Trait for *const Foo {}
-impl Trait for *mut Foo {}
-
-impl Trait for &Foo {}
-impl Trait for &&Foo {}
-impl Trait for &mut Foo {}
-
-impl Trait for [&Foo] {}
-impl Trait for &[Foo] {}
-impl Trait for &*const Foo {}
-
-pub trait Trait2 {
-    fn foo(&self) {}
-}
-
-impl Trait2 for Foo {}
-
-impl Trait2 for [Foo] {}
-impl<const N: usize> Trait2 for [Foo; N] {}
-
-impl Trait2 for *const Foo {}
-impl Trait2 for *mut Foo {}
-
-impl Trait2 for &Foo {}
-impl Trait2 for &&Foo {}
-impl Trait2 for &mut Foo {}
-
-impl Trait2 for [&Foo] {}
-impl Trait2 for &[Foo] {}
-impl Trait2 for &*const Foo {}
-
-fn main() {}
diff --git a/tests/ui/lint/dead-code/unused-impl-for-non-adts.stderr b/tests/ui/lint/dead-code/unused-impl-for-non-adts.stderr
deleted file mode 100644
index e61fc403e81..00000000000
--- a/tests/ui/lint/dead-code/unused-impl-for-non-adts.stderr
+++ /dev/null
@@ -1,20 +0,0 @@
-error: struct `Foo` is never constructed
-  --> $DIR/unused-impl-for-non-adts.rs:3:8
-   |
-LL | struct Foo;
-   |        ^^^
-   |
-note: the lint level is defined here
-  --> $DIR/unused-impl-for-non-adts.rs:1:9
-   |
-LL | #![deny(dead_code)]
-   |         ^^^^^^^^^
-
-error: trait `Trait` is never used
-  --> $DIR/unused-impl-for-non-adts.rs:5:7
-   |
-LL | trait Trait {
-   |       ^^^^^
-
-error: aborting due to 2 previous errors
-