Detect pub structs never constructed

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 +44,25 @@ fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     )
 }
 
+fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: DefId) -> bool {
+    tcx.adt_def(id).all_fields().all(|field| field.vis.is_public())
+}
+
 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)
     {
-        tcx.visibility(def_id).is_public()
-    } else {
-        true
+        return match def_kind {
+            DefKind::Enum | DefKind::Union => tcx.visibility(def_id).is_public(),
+            DefKind::Struct => {
+                tcx.visibility(def_id).is_public() && struct_all_fields_are_public(tcx, def_id)
+            }
+            _ => true,
+        };
     }
+
+    true
 }
 
 /// Determine if a work from the worklist is coming from the a `#[allow]`
@@ -841,6 +850,18 @@ fn create_and_seed_worklist(
             effective_vis
                 .is_public_at_level(Level::Reachable)
                 .then_some(id)
+                .filter(|&id|
+                    // checks impl-of-traits, impl-item-of-trait-items and pub structs with all public fields later
+                    match tcx.def_kind(id) {
+                        DefKind::Impl { of_trait: true } => false,
+                        DefKind::AssocFn => {
+                            let assoc_item = tcx.associated_item(id);
+                            !matches!(assoc_item.container, AssocItemContainer::ImplContainer)
+                                || assoc_item.trait_item_def_id.is_none()
+                        }
+                        DefKind::Struct => struct_all_fields_are_public(tcx, id.to_def_id()),
+                        _ => true
+                    })
                 .map(|id| (id, ComesFromAllowExpect::No))
         })
         // Seed entry point

library/core/src/clone.rs

@@ -184,6 +184,7 @@ pub macro Clone($item:item) {
 //
 // These structs should never appear in user code.
 #[doc(hidden)]
+#[allow(dead_code)]
 #[allow(missing_debug_implementations)]
 #[unstable(
     feature = "derive_clone_copy",
@@ -194,6 +195,7 @@ pub struct AssertParamIsClone<T: Clone + ?Sized> {
     _field: crate::marker::PhantomData<T>,
 }
 #[doc(hidden)]
+#[allow(dead_code)]
 #[allow(missing_debug_implementations)]
 #[unstable(
     feature = "derive_clone_copy",

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> {}

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],

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

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]>);
 

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: (),

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
    |

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

@@ -46,10 +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 {
+pub struct PubStruct2 { //~ ERROR struct `PubStruct2` is never constructed
     #[allow(dead_code)]
     struct_used_as_field: *const StructUsedAsField
 }

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

@@ -22,6 +22,18 @@ 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
    |
@@ -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
 

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

@@ -0,0 +1,17 @@
+#![deny(dead_code)]
+
+pub struct T(()); //~ ERROR struct `T` is never constructed
+
+impl Clone for T {
+    fn clone(&self) -> T {
+        T(())
+    }
+}
+
+pub trait Trait {
+    fn foo(&self) {}
+}
+
+impl Trait for T {}
+
+fn main() {}

tests/ui/lint/dead-code/unused_pub_struct.stderr

@@ -0,0 +1,14 @@
+error: struct `T` is never constructed
+  --> $DIR/unused_pub_struct.rs:3:12
+   |
+LL | pub struct T(());
+   |            ^
+   |
+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
+

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

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

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

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() {}

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() {}

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

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,
 }

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 {

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() {}

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);
 

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);
 

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>
    |         -----     ^^^^^^^^^^^^     ^^^^^^^^^