Rollup merge of #125572 - mu001999-contrib:dead/enhance, r=pnkfelix

Detect pub structs never constructed and unused associated constants

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Lints never constructed public structs.

If we don't provide public methods to construct public structs with private fields, and don't construct them in the local crate. They would be never constructed. So that we can detect such public structs.

---
Update:

Also lints unused associated constants in traits.

32 files changed, 272 insertions, 88 deletions

diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index ddc50e2b811..2cb3c5d8965 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -15,7 +15,7 @@ use rustc_hir::{Node, PatKind, TyKind};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::privacy::Level;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, AssocItemContainer, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
 use rustc_session::lint::builtin::DEAD_CODE;
@@ -44,16 +44,63 @@ fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     )
 }
 
-fn ty_ref_to_pub_struct(tcx: TyCtxt<'_>, ty: &hir::Ty<'_>) -> bool {
+struct Publicness {
+    ty_is_public: bool,
+    ty_and_all_fields_are_public: bool,
+}
+
+impl Publicness {
+    fn new(ty_is_public: bool, ty_and_all_fields_are_public: bool) -> Self {
+        Self { ty_is_public, ty_and_all_fields_are_public }
+    }
+}
+
+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
+    tcx.adt_def(id).all_fields().all(|field| {
+        let field_type = tcx.type_of(field.did).instantiate_identity();
+        if field_type.is_phantom_data() {
+            return true;
+        }
+        let is_positional = field.name.as_str().starts_with(|c: char| c.is_ascii_digit());
+        if is_positional
+            && tcx
+                .layout_of(tcx.param_env(field.did).and(field_type))
+                .map_or(true, |layout| layout.is_zst())
+        {
+            return true;
+        }
+        field.vis.is_public()
+    })
+}
+
+/// check struct and its fields are public or not,
+/// 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()
-        && matches!(def_kind, DefKind::Struct | DefKind::Enum | DefKind::Union)
     {
-        tcx.visibility(def_id).is_public()
-    } else {
-        true
+        return match def_kind {
+            DefKind::Enum | DefKind::Union => {
+                let ty_is_public = tcx.visibility(def_id).is_public();
+                Publicness::new(ty_is_public, ty_is_public)
+            }
+            DefKind::Struct => {
+                let ty_is_public = tcx.visibility(def_id).is_public();
+                Publicness::new(
+                    ty_is_public,
+                    ty_is_public && struct_all_fields_are_public(tcx, def_id),
+                )
+            }
+            _ => Publicness::new(true, true),
+        };
     }
+
+    Publicness::new(true, true)
 }
 
 /// Determine if a work from the worklist is coming from the a `#[allow]`
@@ -427,9 +474,11 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                         {
                             if matches!(trait_item.kind, hir::TraitItemKind::Fn(..))
                                 && !ty_ref_to_pub_struct(self.tcx, impl_ref.self_ty)
+                                    .ty_and_all_fields_are_public
                             {
-                                // skip methods of private ty,
-                                // they would be solved in `solve_rest_impl_items`
+                                // skip impl-items of non pure pub ty,
+                                // cause we don't know the ty is constructed or not,
+                                // check these later in `solve_rest_impl_items`
                                 continue;
                             }
 
@@ -510,22 +559,21 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
             && let Some(local_def_id) = def_id.as_local()
             && matches!(def_kind, DefKind::Struct | DefKind::Enum | DefKind::Union)
         {
-            if self.tcx.visibility(impl_item_id).is_public() {
-                // for the public method, we don't know the trait item is used or not,
-                // so we mark the method live if the self is used
-                return self.live_symbols.contains(&local_def_id);
-            }
-
             if let Some(trait_item_id) = self.tcx.associated_item(impl_item_id).trait_item_def_id
                 && let Some(local_id) = trait_item_id.as_local()
             {
-                // for the private method, we can know the trait item is used or not,
+                // for the local impl item, we can know the trait item is used or not,
                 // so we mark the method live if the self is used and the trait item is used
-                return self.live_symbols.contains(&local_id)
-                    && self.live_symbols.contains(&local_def_id);
+                self.live_symbols.contains(&local_id) && self.live_symbols.contains(&local_def_id)
+            } else {
+                // for the foreign method and inherent pub method,
+                // we don't know the trait item or the method is used or not,
+                // so we mark the method live if the self is used
+                self.live_symbols.contains(&local_def_id)
             }
+        } else {
+            false
         }
-        false
     }
 }
 
@@ -747,7 +795,9 @@ fn check_item<'tcx>(
                 .iter()
                 .filter_map(|def_id| def_id.as_local());
 
-            let ty_is_pub = ty_ref_to_pub_struct(tcx, tcx.hir().item(id).expect_impl().self_ty);
+            let self_ty = tcx.hir().item(id).expect_impl().self_ty;
+            let Publicness { ty_is_public, ty_and_all_fields_are_public } =
+                ty_ref_to_pub_struct(tcx, self_ty);
 
             // And we access the Map here to get HirId from LocalDefId
             for local_def_id in local_def_ids {
@@ -763,18 +813,20 @@ fn check_item<'tcx>(
                 // for trait impl blocks,
                 // mark the method live if the self_ty is public,
                 // or the method is public and may construct self
-                if of_trait
-                    && (!matches!(tcx.def_kind(local_def_id), DefKind::AssocFn)
-                        || tcx.visibility(local_def_id).is_public()
-                            && (ty_is_pub || may_construct_self))
+                if of_trait && matches!(tcx.def_kind(local_def_id), DefKind::AssocTy)
+                    || tcx.visibility(local_def_id).is_public()
+                        && (ty_and_all_fields_are_public || may_construct_self)
                 {
+                    // if the impl item is public,
+                    // and the ty may be constructed or can be constructed in foreign crates,
+                    // mark the impl item live
                     worklist.push((local_def_id, ComesFromAllowExpect::No));
                 } else 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 {
-                    // private method || public method not constructs self
+                } else if of_trait || tcx.visibility(local_def_id).is_public() && ty_is_public {
+                    // private impl items of traits || public impl items not constructs self
                     unsolved_impl_items.push((id, local_def_id));
                 }
             }
@@ -841,6 +893,14 @@ fn create_and_seed_worklist(
             effective_vis
                 .is_public_at_level(Level::Reachable)
                 .then_some(id)
+                .filter(|&id|
+                    // checks impls, impl-items and pub structs with all public fields later
+                    match tcx.def_kind(id) {
+                        DefKind::Impl { .. } => false,
+                        DefKind::AssocConst | DefKind::AssocFn => !matches!(tcx.associated_item(id).container, AssocItemContainer::ImplContainer),
+                        DefKind::Struct => struct_all_fields_are_public(tcx, id.to_def_id()),
+                        _ => true
+                    })
                 .map(|id| (id, ComesFromAllowExpect::No))
         })
         // Seed entry point
@@ -1113,10 +1173,15 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
             || (def_kind == DefKind::Trait && live_symbols.contains(&item.owner_id.def_id))
         {
             for &def_id in tcx.associated_item_def_ids(item.owner_id.def_id) {
-                // We have diagnosed unused methods in traits
+                // We have diagnosed unused assoc consts and fns in traits
                 if matches!(def_kind, DefKind::Impl { of_trait: true })
-                    && tcx.def_kind(def_id) == DefKind::AssocFn
-                    || def_kind == DefKind::Trait && tcx.def_kind(def_id) != DefKind::AssocFn
+                    && matches!(tcx.def_kind(def_id), DefKind::AssocConst | DefKind::AssocFn)
+                    // skip unused public inherent methods,
+                    // cause we have diagnosed unconstructed struct
+                    || matches!(def_kind, DefKind::Impl { of_trait: false })
+                        && tcx.visibility(def_id).is_public()
+                        && ty_ref_to_pub_struct(tcx, tcx.hir().item(item).expect_impl().self_ty).ty_is_public
+                    || def_kind == DefKind::Trait && tcx.def_kind(def_id) == DefKind::AssocTy
                 {
                     continue;
                 }
diff --git a/tests/codegen-units/item-collection/generic-impl.rs b/tests/codegen-units/item-collection/generic-impl.rs
index 23d09e0d8af..b4cd99272b1 100644
--- a/tests/codegen-units/item-collection/generic-impl.rs
+++ b/tests/codegen-units/item-collection/generic-impl.rs
@@ -22,16 +22,16 @@ impl<T> Struct<T> {
     }
 }
 
-pub struct LifeTimeOnly<'a> {
+pub struct _LifeTimeOnly<'a> {
     _a: &'a u32,
 }
 
-impl<'a> LifeTimeOnly<'a> {
-    //~ MONO_ITEM fn LifeTimeOnly::<'_>::foo
+impl<'a> _LifeTimeOnly<'a> {
+    //~ MONO_ITEM fn _LifeTimeOnly::<'_>::foo
     pub fn foo(&self) {}
-    //~ MONO_ITEM fn LifeTimeOnly::<'_>::bar
+    //~ MONO_ITEM fn _LifeTimeOnly::<'_>::bar
     pub fn bar(&'a self) {}
-    //~ MONO_ITEM fn LifeTimeOnly::<'_>::baz
+    //~ MONO_ITEM fn _LifeTimeOnly::<'_>::baz
     pub fn baz<'b>(&'b self) {}
 
     pub fn non_instantiated<T>(&self) {}
diff --git a/tests/codegen-units/item-collection/overloaded-operators.rs b/tests/codegen-units/item-collection/overloaded-operators.rs
index 69b55695d3d..e00e22dbab9 100644
--- a/tests/codegen-units/item-collection/overloaded-operators.rs
+++ b/tests/codegen-units/item-collection/overloaded-operators.rs
@@ -5,44 +5,44 @@
 
 use std::ops::{Add, Deref, Index, IndexMut};
 
-pub struct Indexable {
+pub struct _Indexable {
     data: [u8; 3],
 }
 
-impl Index<usize> for Indexable {
+impl Index<usize> for _Indexable {
     type Output = u8;
 
-    //~ MONO_ITEM fn <Indexable as std::ops::Index<usize>>::index
+    //~ MONO_ITEM fn <_Indexable as std::ops::Index<usize>>::index
     fn index(&self, index: usize) -> &Self::Output {
         if index >= 3 { &self.data[0] } else { &self.data[index] }
     }
 }
 
-impl IndexMut<usize> for Indexable {
-    //~ MONO_ITEM fn <Indexable as std::ops::IndexMut<usize>>::index_mut
+impl IndexMut<usize> for _Indexable {
+    //~ MONO_ITEM fn <_Indexable as std::ops::IndexMut<usize>>::index_mut
     fn index_mut(&mut self, index: usize) -> &mut Self::Output {
         if index >= 3 { &mut self.data[0] } else { &mut self.data[index] }
     }
 }
 
-//~ MONO_ITEM fn <Equatable as std::cmp::PartialEq>::eq
-//~ MONO_ITEM fn <Equatable as std::cmp::PartialEq>::ne
+//~ MONO_ITEM fn <_Equatable as std::cmp::PartialEq>::eq
+//~ MONO_ITEM fn <_Equatable as std::cmp::PartialEq>::ne
 #[derive(PartialEq)]
-pub struct Equatable(u32);
+pub struct _Equatable(u32);
 
-impl Add<u32> for Equatable {
+impl Add<u32> for _Equatable {
     type Output = u32;
 
-    //~ MONO_ITEM fn <Equatable as std::ops::Add<u32>>::add
+    //~ MONO_ITEM fn <_Equatable as std::ops::Add<u32>>::add
     fn add(self, rhs: u32) -> u32 {
         self.0 + rhs
     }
 }
 
-impl Deref for Equatable {
+impl Deref for _Equatable {
     type Target = u32;
 
-    //~ MONO_ITEM fn <Equatable as std::ops::Deref>::deref
+    //~ MONO_ITEM fn <_Equatable as std::ops::Deref>::deref
     fn deref(&self) -> &Self::Target {
         &self.0
     }
diff --git a/tests/ui/coherence/re-rebalance-coherence.rs b/tests/ui/coherence/re-rebalance-coherence.rs
index 9c176d5b1b1..5383a634617 100644
--- a/tests/ui/coherence/re-rebalance-coherence.rs
+++ b/tests/ui/coherence/re-rebalance-coherence.rs
@@ -4,6 +4,7 @@
 extern crate re_rebalance_coherence_lib as lib;
 use lib::*;
 
+#[allow(dead_code)]
 struct Oracle;
 impl Backend for Oracle {}
 impl<'a, T:'a, Tab> QueryFragment<Oracle> for BatchInsert<'a, T, Tab> {}
diff --git a/tests/ui/const-generics/defaults/repr-c-issue-82792.rs b/tests/ui/const-generics/defaults/repr-c-issue-82792.rs
index c23187598bc..4bf2fa761ea 100644
--- a/tests/ui/const-generics/defaults/repr-c-issue-82792.rs
+++ b/tests/ui/const-generics/defaults/repr-c-issue-82792.rs
@@ -2,6 +2,7 @@
 
 //@ run-pass
 
+#[allow(dead_code)]
 #[repr(C)]
 pub struct Loaf<T: Sized, const N: usize = 1> {
     head: [T; N],
diff --git a/tests/ui/const-generics/generic_const_exprs/associated-consts.rs b/tests/ui/const-generics/generic_const_exprs/associated-consts.rs
index 5d2198f50ad..50a6102c605 100644
--- a/tests/ui/const-generics/generic_const_exprs/associated-consts.rs
+++ b/tests/ui/const-generics/generic_const_exprs/associated-consts.rs
@@ -16,7 +16,8 @@ impl BlockCipher for BarCipher {
     const BLOCK_SIZE: usize = 32;
 }
 
-pub struct Block<C>(#[allow(dead_code)] C);
+#[allow(dead_code)]
+pub struct Block<C>(C);
 
 pub fn test<C: BlockCipher, const M: usize>()
 where
diff --git a/tests/ui/const-generics/transparent-maybeunit-array-wrapper.rs b/tests/ui/const-generics/transparent-maybeunit-array-wrapper.rs
index 419d605d0c8..35c41ae4615 100644
--- a/tests/ui/const-generics/transparent-maybeunit-array-wrapper.rs
+++ b/tests/ui/const-generics/transparent-maybeunit-array-wrapper.rs
@@ -6,6 +6,7 @@
 
 use std::mem::MaybeUninit;
 
+#[allow(dead_code)]
 #[repr(transparent)]
 pub struct MaybeUninitWrapper<const N: usize>(MaybeUninit<[u64; N]>);
 
diff --git a/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs b/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs
index 6ab1fb7b039..885dacc727a 100644
--- a/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs
+++ b/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs
@@ -1,9 +1,9 @@
 #![forbid(dead_code)]
 
 #[derive(Debug)]
-pub struct Whatever {
+pub struct Whatever { //~ ERROR struct `Whatever` is never constructed
     pub field0: (),
-    field1: (), //~ ERROR fields `field1`, `field2`, `field3`, and `field4` are never read
+    field1: (),
     field2: (),
     field3: (),
     field4: (),
diff --git a/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr b/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr
index e9b757b6bae..e10d28ad03a 100644
--- a/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr
+++ b/tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr
@@ -1,19 +1,9 @@
-error: fields `field1`, `field2`, `field3`, and `field4` are never read
-  --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:6:5
+error: struct `Whatever` is never constructed
+  --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:4:12
    |
 LL | pub struct Whatever {
-   |            -------- fields in this struct
-LL |     pub field0: (),
-LL |     field1: (),
-   |     ^^^^^^
-LL |     field2: (),
-   |     ^^^^^^
-LL |     field3: (),
-   |     ^^^^^^
-LL |     field4: (),
-   |     ^^^^^^
+   |            ^^^^^^^^
    |
-   = note: `Whatever` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
 note: the lint level is defined here
   --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:1:11
    |
diff --git a/tests/ui/issues/issue-5708.rs b/tests/ui/issues/issue-5708.rs
index ce9ef78ffcd..89ea9fbdcd8 100644
--- a/tests/ui/issues/issue-5708.rs
+++ b/tests/ui/issues/issue-5708.rs
@@ -44,6 +44,7 @@ pub trait MyTrait<T> {
     fn dummy(&self, t: T) -> T { panic!() }
 }
 
+#[allow(dead_code)]
 pub struct MyContainer<'a, T:'a> {
     foos: Vec<&'a (dyn MyTrait<T>+'a)> ,
 }
diff --git a/tests/ui/lint/dead-code/lint-dead-code-1.rs b/tests/ui/lint/dead-code/lint-dead-code-1.rs
index ddcafedf7bc..3386dfa4747 100644
--- a/tests/ui/lint/dead-code/lint-dead-code-1.rs
+++ b/tests/ui/lint/dead-code/lint-dead-code-1.rs
@@ -46,11 +46,10 @@ struct SemiUsedStruct;
 impl SemiUsedStruct {
     fn la_la_la() {}
 }
-struct StructUsedAsField;
+struct StructUsedAsField; //~ ERROR struct `StructUsedAsField` is never constructed
 pub struct StructUsedInEnum;
 struct StructUsedInGeneric;
-pub struct PubStruct2 {
-    #[allow(dead_code)]
+pub struct PubStruct2 { //~ ERROR struct `PubStruct2` is never constructed
     struct_used_as_field: *const StructUsedAsField
 }
 
diff --git a/tests/ui/lint/dead-code/lint-dead-code-1.stderr b/tests/ui/lint/dead-code/lint-dead-code-1.stderr
index eb728b5b930..b0163df8855 100644
--- a/tests/ui/lint/dead-code/lint-dead-code-1.stderr
+++ b/tests/ui/lint/dead-code/lint-dead-code-1.stderr
@@ -22,14 +22,26 @@ error: struct `PrivStruct` is never constructed
 LL | struct PrivStruct;
    |        ^^^^^^^^^^
 
+error: struct `StructUsedAsField` is never constructed
+  --> $DIR/lint-dead-code-1.rs:49:8
+   |
+LL | struct StructUsedAsField;
+   |        ^^^^^^^^^^^^^^^^^
+
+error: struct `PubStruct2` is never constructed
+  --> $DIR/lint-dead-code-1.rs:52:12
+   |
+LL | pub struct PubStruct2 {
+   |            ^^^^^^^^^^
+
 error: enum `priv_enum` is never used
-  --> $DIR/lint-dead-code-1.rs:64:6
+  --> $DIR/lint-dead-code-1.rs:63:6
    |
 LL | enum priv_enum { foo2, bar2 }
    |      ^^^^^^^^^
 
 error: variant `bar3` is never constructed
-  --> $DIR/lint-dead-code-1.rs:67:5
+  --> $DIR/lint-dead-code-1.rs:66:5
    |
 LL | enum used_enum {
    |      --------- variant in this enum
@@ -38,25 +50,25 @@ LL |     bar3
    |     ^^^^
 
 error: function `priv_fn` is never used
-  --> $DIR/lint-dead-code-1.rs:88:4
+  --> $DIR/lint-dead-code-1.rs:87:4
    |
 LL | fn priv_fn() {
    |    ^^^^^^^
 
 error: function `foo` is never used
-  --> $DIR/lint-dead-code-1.rs:93:4
+  --> $DIR/lint-dead-code-1.rs:92:4
    |
 LL | fn foo() {
    |    ^^^
 
 error: function `bar` is never used
-  --> $DIR/lint-dead-code-1.rs:98:4
+  --> $DIR/lint-dead-code-1.rs:97:4
    |
 LL | fn bar() {
    |    ^^^
 
 error: function `baz` is never used
-  --> $DIR/lint-dead-code-1.rs:102:4
+  --> $DIR/lint-dead-code-1.rs:101:4
    |
 LL | fn baz() -> impl Copy {
    |    ^^^
@@ -67,5 +79,5 @@ error: struct `Bar` is never constructed
 LL |     pub struct Bar;
    |                ^^^
 
-error: aborting due to 10 previous errors
+error: aborting due to 12 previous errors
 
diff --git a/tests/ui/lint/dead-code/unused-assoc-const.rs b/tests/ui/lint/dead-code/unused-assoc-const.rs
new file mode 100644
index 00000000000..36e8315ad36
--- /dev/null
+++ b/tests/ui/lint/dead-code/unused-assoc-const.rs
@@ -0,0 +1,20 @@
+#![deny(dead_code)]
+
+trait Trait {
+    const UNUSED_CONST: i32; //~ ERROR associated constant `UNUSED_CONST` is never used
+    const USED_CONST: i32;
+
+    fn foo(&self) {}
+}
+
+pub struct T(());
+
+impl Trait for T {
+    const UNUSED_CONST: i32 = 0;
+    const USED_CONST: i32 = 1;
+}
+
+fn main() {
+    T(()).foo();
+    T::USED_CONST;
+}
diff --git a/tests/ui/lint/dead-code/unused-assoc-const.stderr b/tests/ui/lint/dead-code/unused-assoc-const.stderr
new file mode 100644
index 00000000000..78296d70663
--- /dev/null
+++ b/tests/ui/lint/dead-code/unused-assoc-const.stderr
@@ -0,0 +1,16 @@
+error: associated constant `UNUSED_CONST` is never used
+  --> $DIR/unused-assoc-const.rs:4:11
+   |
+LL | trait Trait {
+   |       ----- associated constant in this trait
+LL |     const UNUSED_CONST: i32;
+   |           ^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-assoc-const.rs:1:9
+   |
+LL | #![deny(dead_code)]
+   |         ^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/lint/dead-code/unused-pub-struct.rs b/tests/ui/lint/dead-code/unused-pub-struct.rs
new file mode 100644
index 00000000000..aaf4dd612de
--- /dev/null
+++ b/tests/ui/lint/dead-code/unused-pub-struct.rs
@@ -0,0 +1,48 @@
+#![deny(dead_code)]
+
+pub struct NotLint1(());
+pub struct NotLint2(std::marker::PhantomData<i32>);
+
+pub struct NeverConstructed(i32); //~ ERROR struct `NeverConstructed` is never constructed
+
+impl NeverConstructed {
+    pub fn not_construct_self(&self) {}
+}
+
+impl Clone for NeverConstructed {
+    fn clone(&self) -> NeverConstructed {
+        NeverConstructed(0)
+    }
+}
+
+pub trait Trait {
+    fn not_construct_self(&self);
+}
+
+impl Trait for NeverConstructed {
+    fn not_construct_self(&self) {
+        self.0;
+    }
+}
+
+pub struct Constructed(i32);
+
+impl Constructed {
+    pub fn construct_self() -> Self {
+        Constructed(0)
+    }
+}
+
+impl Clone for Constructed {
+    fn clone(&self) -> Constructed {
+        Constructed(0)
+    }
+}
+
+impl Trait for Constructed {
+    fn not_construct_self(&self) {
+        self.0;
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/lint/dead-code/unused-pub-struct.stderr b/tests/ui/lint/dead-code/unused-pub-struct.stderr
new file mode 100644
index 00000000000..3667ddb97bd
--- /dev/null
+++ b/tests/ui/lint/dead-code/unused-pub-struct.stderr
@@ -0,0 +1,14 @@
+error: struct `NeverConstructed` is never constructed
+  --> $DIR/unused-pub-struct.rs:6:12
+   |
+LL | pub struct NeverConstructed(i32);
+   |            ^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-pub-struct.rs:1:9
+   |
+LL | #![deny(dead_code)]
+   |         ^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.fixed b/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.fixed
index a851300a982..e9c89807fa5 100644
--- a/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.fixed
+++ b/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.fixed
@@ -1,7 +1,8 @@
 // Regression test for issues #100790 and #106439.
 //@ run-rustfix
 
-pub struct Example(#[allow(dead_code)] usize)
+#[allow(dead_code)]
+pub struct Example(usize)
 where
     (): Sized;
 //~^^^ ERROR where clauses are not allowed before tuple struct bodies
diff --git a/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.rs b/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.rs
index 10f435859f1..3bd0f51ec2c 100644
--- a/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.rs
+++ b/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.rs
@@ -1,10 +1,11 @@
 // Regression test for issues #100790 and #106439.
 //@ run-rustfix
 
+#[allow(dead_code)]
 pub struct Example
 where
     (): Sized,
-(#[allow(dead_code)] usize);
+(usize);
 //~^^^ ERROR where clauses are not allowed before tuple struct bodies
 
 struct _Demo
diff --git a/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.stderr b/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.stderr
index ddbf237e866..77eafa6bea3 100644
--- a/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.stderr
+++ b/tests/ui/parser/recover/recover-where-clause-before-tuple-struct-body-0.stderr
@@ -1,23 +1,23 @@
 error: where clauses are not allowed before tuple struct bodies
-  --> $DIR/recover-where-clause-before-tuple-struct-body-0.rs:5:1
+  --> $DIR/recover-where-clause-before-tuple-struct-body-0.rs:6:1
    |
 LL |   pub struct Example
    |              ------- while parsing this tuple struct
 LL | / where
 LL | |     (): Sized,
    | |______________^ unexpected where clause
-LL |   (#[allow(dead_code)] usize);
-   |   --------------------------- the struct body
+LL |   (usize);
+   |   ------- the struct body
    |
 help: move the body before the where clause
    |
-LL ~ pub struct Example(#[allow(dead_code)] usize)
+LL ~ pub struct Example(usize)
 LL | where
 LL ~     (): Sized;
    |
 
 error: where clauses are not allowed before tuple struct bodies
-  --> $DIR/recover-where-clause-before-tuple-struct-body-0.rs:11:1
+  --> $DIR/recover-where-clause-before-tuple-struct-body-0.rs:12:1
    |
 LL |   struct _Demo
    |          ----- while parsing this tuple struct
diff --git a/tests/ui/pub/pub-ident-struct-4.fixed b/tests/ui/pub/pub-ident-struct-4.fixed
index 5fedbb72437..a62ece43ece 100644
--- a/tests/ui/pub/pub-ident-struct-4.fixed
+++ b/tests/ui/pub/pub-ident-struct-4.fixed
@@ -1,6 +1,7 @@
 //@ run-rustfix
 
-pub struct T(#[allow(dead_code)] String);
+#[allow(dead_code)]
+pub struct T(String);
 //~^ ERROR missing `struct` for struct definition
 
 fn main() {}
diff --git a/tests/ui/pub/pub-ident-struct-4.rs b/tests/ui/pub/pub-ident-struct-4.rs
index 5c721c25a78..0d56a31beaf 100644
--- a/tests/ui/pub/pub-ident-struct-4.rs
+++ b/tests/ui/pub/pub-ident-struct-4.rs
@@ -1,6 +1,7 @@
 //@ run-rustfix
 
-pub T(#[allow(dead_code)] String);
+#[allow(dead_code)]
+pub T(String);
 //~^ ERROR missing `struct` for struct definition
 
 fn main() {}
diff --git a/tests/ui/pub/pub-ident-struct-4.stderr b/tests/ui/pub/pub-ident-struct-4.stderr
index 5fbb02c8673..ec136783211 100644
--- a/tests/ui/pub/pub-ident-struct-4.stderr
+++ b/tests/ui/pub/pub-ident-struct-4.stderr
@@ -1,12 +1,12 @@
 error: missing `struct` for struct definition
-  --> $DIR/pub-ident-struct-4.rs:3:4
+  --> $DIR/pub-ident-struct-4.rs:4:4
    |
-LL | pub T(#[allow(dead_code)] String);
+LL | pub T(String);
    |    ^
    |
 help: add `struct` here to parse `T` as a public struct
    |
-LL | pub struct T(#[allow(dead_code)] String);
+LL | pub struct T(String);
    |     ++++++
 
 error: aborting due to 1 previous error
diff --git a/tests/ui/regions/regions-issue-21422.rs b/tests/ui/regions/regions-issue-21422.rs
index 54beed9b3ac..67852a6f5de 100644
--- a/tests/ui/regions/regions-issue-21422.rs
+++ b/tests/ui/regions/regions-issue-21422.rs
@@ -5,6 +5,7 @@
 
 //@ pretty-expanded FIXME #23616
 
+#[allow(dead_code)]
 pub struct P<'a> {
     _ptr: *const &'a u8,
 }
diff --git a/tests/ui/structs-enums/newtype-struct-with-dtor.rs b/tests/ui/structs-enums/newtype-struct-with-dtor.rs
index 19672e41c9a..16439a7fedd 100644
--- a/tests/ui/structs-enums/newtype-struct-with-dtor.rs
+++ b/tests/ui/structs-enums/newtype-struct-with-dtor.rs
@@ -3,8 +3,10 @@
 #![allow(unused_variables)]
 //@ pretty-expanded FIXME #23616
 
+#[allow(dead_code)]
 pub struct Fd(u32);
 
+#[allow(dead_code)]
 fn foo(a: u32) {}
 
 impl Drop for Fd {
diff --git a/tests/ui/structs-enums/uninstantiable-struct.rs b/tests/ui/structs-enums/uninstantiable-struct.rs
index 97bc7d8414e..1074dbcd6e6 100644
--- a/tests/ui/structs-enums/uninstantiable-struct.rs
+++ b/tests/ui/structs-enums/uninstantiable-struct.rs
@@ -1,4 +1,5 @@
 //@ run-pass
-pub struct Z(#[allow(dead_code)] &'static Z);
+#[allow(dead_code)]
+pub struct Z(&'static Z);
 
 pub fn main() {}
diff --git a/tests/ui/suggestions/derive-clone-for-eq.fixed b/tests/ui/suggestions/derive-clone-for-eq.fixed
index 4dc362f9478..cf800c6e47d 100644
--- a/tests/ui/suggestions/derive-clone-for-eq.fixed
+++ b/tests/ui/suggestions/derive-clone-for-eq.fixed
@@ -1,6 +1,7 @@
 //@ run-rustfix
 // https://github.com/rust-lang/rust/issues/79076
 
+#[allow(dead_code)]
 #[derive(Clone, Eq)] //~ ERROR [E0277]
 pub struct Struct<T: std::clone::Clone>(T);
 
diff --git a/tests/ui/suggestions/derive-clone-for-eq.rs b/tests/ui/suggestions/derive-clone-for-eq.rs
index b3635000f16..84736426bac 100644
--- a/tests/ui/suggestions/derive-clone-for-eq.rs
+++ b/tests/ui/suggestions/derive-clone-for-eq.rs
@@ -1,6 +1,7 @@
 //@ run-rustfix
 // https://github.com/rust-lang/rust/issues/79076
 
+#[allow(dead_code)]
 #[derive(Clone, Eq)] //~ ERROR [E0277]
 pub struct Struct<T>(T);
 
diff --git a/tests/ui/suggestions/derive-clone-for-eq.stderr b/tests/ui/suggestions/derive-clone-for-eq.stderr
index 6fae6e1316d..54670fbffcf 100644
--- a/tests/ui/suggestions/derive-clone-for-eq.stderr
+++ b/tests/ui/suggestions/derive-clone-for-eq.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `T: Clone` is not satisfied
-  --> $DIR/derive-clone-for-eq.rs:4:17
+  --> $DIR/derive-clone-for-eq.rs:5:17
    |
 LL | #[derive(Clone, Eq)]
    |                 ^^ the trait `Clone` is not implemented for `T`, which is required by `Struct<T>: PartialEq`
    |
 note: required for `Struct<T>` to implement `PartialEq`
-  --> $DIR/derive-clone-for-eq.rs:7:19
+  --> $DIR/derive-clone-for-eq.rs:8:19
    |
 LL | impl<T: Clone, U> PartialEq<U> for Struct<T>
    |         -----     ^^^^^^^^^^^^     ^^^^^^^^^
diff --git a/tests/ui/suggestions/option-content-move.fixed b/tests/ui/suggestions/option-content-move.fixed
index 4a5a9483c20..ef07d55871e 100644
--- a/tests/ui/suggestions/option-content-move.fixed
+++ b/tests/ui/suggestions/option-content-move.fixed
@@ -1,4 +1,5 @@
 //@ run-rustfix
+#[allow(dead_code)]
 pub struct LipogramCorpora {
     selections: Vec<(char, Option<String>)>,
 }
@@ -17,6 +18,7 @@ impl LipogramCorpora {
     }
 }
 
+#[allow(dead_code)]
 pub struct LipogramCorpora2 {
     selections: Vec<(char, Result<String, String>)>,
 }
diff --git a/tests/ui/suggestions/option-content-move.rs b/tests/ui/suggestions/option-content-move.rs
index 90d05c74399..5be6358fd6a 100644
--- a/tests/ui/suggestions/option-content-move.rs
+++ b/tests/ui/suggestions/option-content-move.rs
@@ -1,4 +1,5 @@
 //@ run-rustfix
+#[allow(dead_code)]
 pub struct LipogramCorpora {
     selections: Vec<(char, Option<String>)>,
 }
@@ -17,6 +18,7 @@ impl LipogramCorpora {
     }
 }
 
+#[allow(dead_code)]
 pub struct LipogramCorpora2 {
     selections: Vec<(char, Result<String, String>)>,
 }
diff --git a/tests/ui/suggestions/option-content-move.stderr b/tests/ui/suggestions/option-content-move.stderr
index a382a04344a..b4ec5b180d2 100644
--- a/tests/ui/suggestions/option-content-move.stderr
+++ b/tests/ui/suggestions/option-content-move.stderr
@@ -1,5 +1,5 @@
 error[E0507]: cannot move out of `selection.1` which is behind a shared reference
-  --> $DIR/option-content-move.rs:10:20
+  --> $DIR/option-content-move.rs:11:20
    |
 LL |                 if selection.1.unwrap().contains(selection.0) {
    |                    ^^^^^^^^^^^ -------- `selection.1` moved due to this method call
@@ -19,7 +19,7 @@ LL |                 if selection.1.clone().unwrap().contains(selection.0) {
    |                               ++++++++
 
 error[E0507]: cannot move out of `selection.1` which is behind a shared reference
-  --> $DIR/option-content-move.rs:28:20
+  --> $DIR/option-content-move.rs:30:20
    |
 LL |                 if selection.1.unwrap().contains(selection.0) {
    |                    ^^^^^^^^^^^ -------- `selection.1` moved due to this method call
diff --git a/tests/ui/traits/object/generics.rs b/tests/ui/traits/object/generics.rs
index 462b0bc5bb7..0ae562c0d30 100644
--- a/tests/ui/traits/object/generics.rs
+++ b/tests/ui/traits/object/generics.rs
@@ -7,6 +7,7 @@ pub trait Trait2<A> {
     fn doit(&self) -> A;
 }
 
+#[allow(dead_code)]
 pub struct Impl<A1, A2, A3> {
     m1: marker::PhantomData<(A1,A2,A3)>,
     /*