Extend rules of dead code analysis for impls for adts to impls for types refer to adts

compiler/rustc_passes/src/dead.rs

@@ -54,7 +54,24 @@ impl Publicness {
     }
 }
 
-fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> bool {
+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 {
     // 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
@@ -79,10 +96,7 @@ fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> 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 TyKind::Path(hir::QPath::Resolved(_, path)) = ty.kind
-        && let Res::Def(def_kind, def_id) = path.res
-        && def_id.is_local()
-    {
+    if let Some((def_id, def_kind)) = adt_of(ty) {
         return match def_kind {
             DefKind::Enum | DefKind::Union => {
                 let ty_is_public = tcx.visibility(def_id).is_public();
@@ -584,10 +598,8 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
     }
 
     fn impl_item_with_used_self(&mut self, impl_id: hir::ItemId, impl_item_id: LocalDefId) -> bool {
-        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()
+        if let Some((local_def_id, def_kind)) =
+            adt_of(self.tcx.hir().item(impl_id).expect_impl().self_ty)
             && 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
@@ -931,7 +943,7 @@ 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.to_def_id()) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
+                        DefKind::Struct => struct_all_fields_are_public(tcx, id) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
                         _ => true
                     })
                 .map(|id| (id, ComesFromAllowExpect::No))

tests/ui/lint/dead-code/unused-impl-for-non-adts.rs

@@ -0,0 +1,45 @@
+#![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() {}

tests/ui/lint/dead-code/unused-impl-for-non-adts.stderr

@@ -0,0 +1,20 @@
+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
+