Revert recent changes to dead code analysis (this time, stable)

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, AssocItemContainer, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
 use rustc_session::lint::builtin::DEAD_CODE;
@@ -44,63 +44,16 @@ fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> 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 {
+fn ty_ref_to_pub_struct(tcx: TyCtxt<'_>, ty: &hir::Ty<'_>) -> bool {
     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)
     {
-        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),
-        };
+        tcx.visibility(def_id).is_public()
+    } else {
+        true
     }
-
-    Publicness::new(true, true)
 }
 
 /// Determine if a work from the worklist is coming from the a `#[allow]`
@@ -474,11 +427,9 @@ 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 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`
+                                // skip methods of private ty,
+                                // they would be solved in `solve_rest_impl_items`
                                 continue;
                             }
 
@@ -559,21 +510,22 @@ 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 local impl item, we can know the trait item is used or not,
+                // for the private method, 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
-                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)
+                return self.live_symbols.contains(&local_id)
+                    && self.live_symbols.contains(&local_def_id);
             }
-        } else {
-            false
         }
+        false
     }
 }
 
@@ -795,9 +747,7 @@ fn check_item<'tcx>(
                 .iter()
                 .filter_map(|def_id| def_id.as_local());
 
-            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);
+            let ty_is_pub = ty_ref_to_pub_struct(tcx, tcx.hir().item(id).expect_impl().self_ty);
 
             // And we access the Map here to get HirId from LocalDefId
             for local_def_id in local_def_ids {
@@ -813,20 +763,18 @@ 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::AssocTy)
-                    || tcx.visibility(local_def_id).is_public()
-                        && (ty_and_all_fields_are_public || 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 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 || tcx.visibility(local_def_id).is_public() && ty_is_public {
-                    // private impl items of traits || public impl items not constructs self
+                } else if of_trait {
+                    // private method || public method not constructs self
                     unsolved_impl_items.push((id, local_def_id));
                 }
             }
@@ -893,14 +841,6 @@ 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()) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
-                        _ => true
-                    })
                 .map(|id| (id, ComesFromAllowExpect::No))
         })
         // Seed entry point
@@ -1173,15 +1113,10 @@ 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 assoc consts and fns in traits
+                // We have diagnosed unused methods in traits
                 if matches!(def_kind, DefKind::Impl { of_trait: true })
-                    && 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
+                    && tcx.def_kind(def_id) == DefKind::AssocFn
+                    || def_kind == DefKind::Trait && tcx.def_kind(def_id) != DefKind::AssocFn
                 {
                     continue;
                 }

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) {}

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
     }

tests/ui/coherence/re-rebalance-coherence.rs

@@ -4,7 +4,6 @@
 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> {}

tests/ui/const-generics/defaults/repr-c-issue-82792.rs

@@ -2,7 +2,6 @@
 
 //@ run-pass
 
-#[allow(dead_code)]
 #[repr(C)]
 pub struct Loaf<T: Sized, const N: usize = 1> {
     head: [T; N],

tests/ui/const-generics/generic_const_exprs/associated-consts.rs

@@ -16,8 +16,7 @@ impl BlockCipher for BarCipher {
     const BLOCK_SIZE: usize = 32;
 }
 
-#[allow(dead_code)]
-pub struct Block<C>(C);
+pub struct Block<C>(#[allow(dead_code)] C);
 
 pub fn test<C: BlockCipher, const M: usize>()
 where

tests/ui/const-generics/transparent-maybeunit-array-wrapper.rs

@@ -6,7 +6,6 @@
 
 use std::mem::MaybeUninit;
 
-#[allow(dead_code)]
 #[repr(transparent)]
 pub struct MaybeUninitWrapper<const N: usize>(MaybeUninit<[u64; N]>);
 

tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs

@@ -1,9 +1,9 @@
 #![forbid(dead_code)]
 
 #[derive(Debug)]
-pub struct Whatever { //~ ERROR struct `Whatever` is never constructed
+pub struct Whatever {
     pub field0: (),
-    field1: (),
+    field1: (), //~ ERROR fields `field1`, `field2`, `field3`, and `field4` are never read
     field2: (),
     field3: (),
     field4: (),

tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr

@@ -1,9 +1,19 @@
-error: struct `Whatever` is never constructed
-  --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:4:12
+error: fields `field1`, `field2`, `field3`, and `field4` are never read
+  --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:6:5
    |
 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
    |

tests/ui/issues/issue-5708.rs

@@ -44,7 +44,6 @@ 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)> ,
 }

tests/ui/lint/dead-code/lint-dead-code-1.rs

@@ -46,10 +46,11 @@ struct SemiUsedStruct;
 impl SemiUsedStruct {
     fn la_la_la() {}
 }
-struct StructUsedAsField; //~ ERROR struct `StructUsedAsField` is never constructed
+struct StructUsedAsField;
 pub struct StructUsedInEnum;
 struct StructUsedInGeneric;
-pub struct PubStruct2 { //~ ERROR struct `PubStruct2` is never constructed
+pub struct PubStruct2 {
+    #[allow(dead_code)]
     struct_used_as_field: *const StructUsedAsField
 }