Merge unused_tuple_struct_fields into dead_code

This implicitly upgrades the lint from `allow` to `warn` and places it
into the `unused` lint group.

Author: shepmaster

compiler/rustc_lint_defs/src/builtin.rs

@@ -569,8 +569,13 @@ declare_lint! {
     /// Dead code may signal a mistake or unfinished code. To silence the
     /// warning for individual items, prefix the name with an underscore such
     /// as `_foo`. If it was intended to expose the item outside of the crate,
-    /// consider adding a visibility modifier like `pub`. Otherwise consider
-    /// removing the unused code.
+    /// consider adding a visibility modifier like `pub`.
+    ///
+    /// To preserve the numbering of tuple structs with unused fields,
+    /// change the unused fields to have unit type or use
+    /// `PhantomData`.
+    ///
+    /// Otherwise consider removing the unused code.
     pub DEAD_CODE,
     Warn,
     "detect unused, unexported items"
@@ -604,32 +609,6 @@ declare_lint! {
     "detects attributes that were not used by the compiler"
 }
 
-declare_lint! {
-    /// The `unused_tuple_struct_fields` lint detects fields of tuple structs
-    /// that are never read.
-    ///
-    /// ### Example
-    ///
-    /// ```rust
-    /// #[warn(unused_tuple_struct_fields)]
-    /// struct S(i32, i32, i32);
-    /// let s = S(1, 2, 3);
-    /// let _ = (s.0, s.2);
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// Tuple struct fields that are never read anywhere may indicate a
-    /// mistake or unfinished code. To silence this warning, consider
-    /// removing the unused field(s) or, to preserve the numbering of the
-    /// remaining fields, change the unused field(s) to have unit type.
-    pub UNUSED_TUPLE_STRUCT_FIELDS,
-    Allow,
-    "detects tuple struct fields that are never read"
-}
-
 declare_lint! {
     /// The `unreachable_code` lint detects unreachable code paths.
     ///
@@ -3466,7 +3445,6 @@ declare_lint_pass! {
         UNUSED_MACROS,
         UNUSED_MUT,
         UNUSED_QUALIFICATIONS,
-        UNUSED_TUPLE_STRUCT_FIELDS,
         UNUSED_UNSAFE,
         UNUSED_VARIABLES,
         USELESS_DEPRECATED,

compiler/rustc_passes/src/dead.rs

@@ -835,12 +835,6 @@ impl<'tcx> DeadVisitor<'tcx> {
         let multiple = num > 6;
         let name_list = names.into();
 
-        let lint = if is_positional {
-            lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS
-        } else {
-            lint::builtin::DEAD_CODE
-        };
-
         let parent_info = if let Some(parent_item) = parent_item {
             let parent_descr = tcx.def_descr(parent_item.to_def_id());
             let span = if let DefKind::Impl { .. } = tcx.def_kind(parent_item) {
@@ -893,7 +887,12 @@ impl<'tcx> DeadVisitor<'tcx> {
             }
         };
 
-        self.tcx.emit_spanned_lint(lint, first_hir_id, MultiSpan::from_spans(spans), diag);
+        self.tcx.emit_spanned_lint(
+            lint::builtin::DEAD_CODE,
+            first_hir_id,
+            MultiSpan::from_spans(spans),
+            diag,
+        );
     }
 
     fn warn_multiple(
@@ -1013,17 +1012,11 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
                         if let ShouldWarnAboutField::Yes(is_pos) =
                             visitor.should_warn_about_field(field)
                         {
-                            let level = tcx
-                                .lint_level_at_node(
-                                    if is_pos {
-                                        is_positional = true;
-                                        lint::builtin::UNUSED_TUPLE_STRUCT_FIELDS
-                                    } else {
-                                        lint::builtin::DEAD_CODE
-                                    },
-                                    hir_id,
-                                )
-                                .0;
+                            if is_pos {
+                                is_positional = true;
+                            }
+
+                            let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
                             Some(DeadItem { def_id, name: field.name, level })
                         } else {
                             None

library/alloc/src/boxed.rs

@@ -24,6 +24,7 @@
 //! Creating a recursive data structure:
 //!
 //! ```
+//! ##[allow(dead_code)]
 //! #[derive(Debug)]
 //! enum List<T> {
 //!     Cons(T, Box<List<T>>),

library/alloc/src/boxed/thin.rs

@@ -171,7 +171,7 @@ struct WithHeader<H>(NonNull<u8>, PhantomData<H>);
 /// An opaque representation of `WithHeader<H>` to avoid the
 /// projection invariance of `<T as Pointee>::Metadata`.
 #[repr(transparent)]
-#[allow(unused_tuple_struct_fields)] // Field only used through `WithHeader` type above.
+#[allow(dead_code)] // Field only used through `WithHeader` type above.
 struct WithOpaqueHeader(NonNull<u8>);
 
 impl WithOpaqueHeader {

library/alloc/src/collections/btree/set/tests.rs

@@ -527,7 +527,7 @@ fn test_extend_ref() {
 #[test]
 fn test_recovery() {
     #[derive(Debug)]
-    struct Foo(&'static str, i32);
+    struct Foo(&'static str, #[allow(dead_code)] i32);
 
     impl PartialEq for Foo {
         fn eq(&self, other: &Self) -> bool {

library/alloc/src/collections/vec_deque/tests.rs

@@ -1085,7 +1085,7 @@ fn test_clone_from() {
 fn test_vec_deque_truncate_drop() {
     static mut DROPS: u32 = 0;
     #[derive(Clone)]
-    struct Elem(i32);
+    struct Elem(#[allow(dead_code)] i32);
     impl Drop for Elem {
         fn drop(&mut self) {
             unsafe {

library/alloc/tests/autotraits.rs

@@ -1,7 +1,7 @@
 fn require_sync<T: Sync>(_: T) {}
 fn require_send_sync<T: Send + Sync>(_: T) {}
 
-struct NotSend(*const ());
+struct NotSend(#[allow(dead_code)] *const ());
 unsafe impl Sync for NotSend {}
 
 #[test]

library/alloc/tests/vec.rs

@@ -549,7 +549,7 @@ fn test_cmp() {
 #[test]
 fn test_vec_truncate_drop() {
     static mut DROPS: u32 = 0;
-    struct Elem(i32);
+    struct Elem(#[allow(dead_code)] i32);
     impl Drop for Elem {
         fn drop(&mut self) {
             unsafe {
@@ -1091,7 +1091,7 @@ fn test_into_iter_advance_by() {
 
 #[test]
 fn test_into_iter_drop_allocator() {
-    struct ReferenceCountedAllocator<'a>(DropCounter<'a>);
+    struct ReferenceCountedAllocator<'a>(#[allow(dead_code)] DropCounter<'a>);
 
     unsafe impl Allocator for ReferenceCountedAllocator<'_> {
         fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, core::alloc::AllocError> {
@@ -2401,7 +2401,7 @@ fn test_vec_dedup_multiple_ident() {
 #[test]
 fn test_vec_dedup_partialeq() {
     #[derive(Debug)]
-    struct Foo(i32, i32);
+    struct Foo(i32, #[allow(dead_code)] i32);
 
     impl PartialEq for Foo {
         fn eq(&self, other: &Foo) -> bool {

library/core/benches/slice.rs

@@ -91,7 +91,7 @@ fn binary_search_l3_worst_case(b: &mut Bencher) {
 }
 
 #[derive(Clone)]
-struct Rgb(u8, u8, u8);
+struct Rgb(#[allow(dead_code)] u8, #[allow(dead_code)] u8, #[allow(dead_code)] u8);
 
 impl Rgb {
     fn gen(i: usize) -> Self {
@@ -154,7 +154,7 @@ swap_with_slice!(swap_with_slice_5x_usize_3000, 3000, |i| [i; 5]);
 #[bench]
 fn fill_byte_sized(b: &mut Bencher) {
     #[derive(Copy, Clone)]
-    struct NewType(u8);
+    struct NewType(#[allow(dead_code)] u8);
 
     let mut ary = [NewType(0); 1024];
 

library/core/tests/any.rs

@@ -122,7 +122,7 @@ fn any_unsized() {
 fn distinct_type_names() {
     // https://github.com/rust-lang/rust/issues/84666
 
-    struct Velocity(f32, f32);
+    struct Velocity(#[allow(dead_code)] f32, #[allow(dead_code)] f32);
 
     fn type_name_of_val<T>(_: T) -> &'static str {
         type_name::<T>()