Fix new dead_code instances in compiler

Author: GrigorenkoPV

compiler/rustc_builtin_macros/src/format_foreign.rs

@@ -62,6 +62,8 @@ pub(crate) mod printf {
         /// Precision of the conversion.
         precision: Option<Num>,
         /// Length modifier for the conversion.
+        // FIXME(#143487): is it okay that this field is never read?
+        #[cfg_attr(not(bootstrap), expect(dead_code))]
         length: Option<&'a str>,
         /// Type of parameter being converted.
         type_: &'a str,

compiler/rustc_data_structures/src/sync/worker_local.rs

@@ -12,7 +12,13 @@ use crate::sync::CacheAligned;
 /// A pointer to the `RegistryData` which uniquely identifies a registry.
 /// This identifier can be reused if the registry gets freed.
 #[derive(Clone, Copy, PartialEq)]
-struct RegistryId(*const RegistryData);
+struct RegistryId(
+    #[cfg_attr(
+        not(bootstrap),
+        expect(dead_code, reason = "This field is only used for equality comparisons")
+    )]
+    *const RegistryData,
+);
 
 impl RegistryId {
     #[inline(always)]

compiler/rustc_hir_typeck/src/loops.rs

@@ -26,15 +26,21 @@ use crate::errors::{
 enum Context {
     Normal,
     Fn,
-    Loop(hir::LoopSource),
+    Loop(
+        // FIXME(#143487): is it okay that this field is never read?
+        #[cfg_attr(not(bootstrap), expect(dead_code))] hir::LoopSource,
+    ),
     Closure(Span),
     Coroutine {
         coroutine_span: Span,
         kind: hir::CoroutineDesugaring,
         source: hir::CoroutineSource,
     },
     UnlabeledBlock(Span),
-    UnlabeledIfBlock(Span),
+    UnlabeledIfBlock(
+        // FIXME(#143487): is it okay that this field is never read?
+        #[cfg_attr(not(bootstrap), expect(dead_code))] Span,
+    ),
     LabeledBlock,
     /// E.g. The labeled block inside `['_'; 'block: { break 'block 1 + 2; }]`.
     AnonConst,

compiler/rustc_pattern_analysis/src/constructor.rs

@@ -657,7 +657,13 @@ impl Slice {
 
 /// A globally unique id to distinguish `Opaque` patterns.
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct OpaqueId(u32);
+pub struct OpaqueId(
+    #[cfg_attr(
+        not(bootstrap),
+        expect(dead_code, reason = "This field is only used for equality comparisons")
+    )]
+    u32,
+);
 
 impl OpaqueId {
     pub fn new() -> Self {