Auto merge of rust-lang#118297 - shepmaster:warn-dead-tuple-fields, r=WaffleLapkin

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.

[Discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Moving.20.60unused_tuple_struct_fields.60.20from.20allow.20to.20warn)

Author: bors

compiler/rustc_lint/src/lib.rs

@@ -328,6 +328,7 @@ fn register_builtins(store: &mut LintStore) {
     store.register_renamed("disjoint_capture_migration", "rust_2021_incompatible_closure_captures");
     store.register_renamed("or_patterns_back_compat", "rust_2021_incompatible_or_patterns");
     store.register_renamed("non_fmt_panic", "non_fmt_panics");
+    store.register_renamed("unused_tuple_struct_fields", "dead_code");
 
     // These were moved to tool lints, but rustc still sees them when compiling normally, before
     // tool lints are registered, so `check_tool_name_for_backwards_compat` doesn't work. Use

compiler/rustc_lint_defs/src/builtin.rs

@@ -125,7 +125,6 @@ declare_lint_pass! {
         UNUSED_MACROS,
         UNUSED_MUT,
         UNUSED_QUALIFICATIONS,
-        UNUSED_TUPLE_STRUCT_FIELDS,
         UNUSED_UNSAFE,
         UNUSED_VARIABLES,
         USELESS_DEPRECATED,
@@ -697,8 +696,13 @@ 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"
@@ -732,32 +736,6 @@ 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.
     ///