Implement unused_pub_items_in_binary lint

Author: mu001999

compiler/rustc_lint_defs/src/builtin.rs

@@ -145,6 +145,7 @@ declare_lint_pass! {
         UNUSED_MACROS,
         UNUSED_MACRO_RULES,
         UNUSED_MUT,
+        UNUSED_PUB_ITEMS_IN_BINARY,
         UNUSED_QUALIFICATIONS,
         UNUSED_UNSAFE,
         UNUSED_VARIABLES,
@@ -781,6 +782,29 @@ declare_lint! {
     "detect unused, unexported items"
 }
 
+declare_lint! {
+    /// The `unused_pub_items_in_binary` lint detects public items in executable
+    /// crates that are not used.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// pub fn helper() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// In executable crates, `pub` items are often not part of a public API.
+    /// This lint helps detect such items when they are never used within the
+    /// crate.
+    pub UNUSED_PUB_ITEMS_IN_BINARY,
+    Allow,
+    "detect public items in executable crates that are never used",
+    crate_level_only
+}
+
 declare_lint! {
     /// The `unused_attributes` lint detects attributes that were not used by
     /// the compiler.

compiler/rustc_middle/src/queries.rs

@@ -1190,10 +1190,16 @@ rustc_queries! {
         cache_on_disk_if { tcx.is_typeck_child(key.to_def_id()) }
     }
 
-    /// Return the live symbols in the crate for dead code check.
+    /// Return the live symbols in the crate for dead code checks.
     ///
-    /// The second return value maps from ADTs to ignored derived traits (e.g. Debug and Clone).
+    /// The return values are:
+    /// - phase-1 live symbols (before reachable-public dead-code seeding)
+    /// - final live symbols for dead-code
+    /// - unused reachable public symbols in executable crates
+    /// - a map from ADTs to ignored derived traits (e.g. Debug and Clone)
     query live_symbols_and_ignored_derived_traits(_: ()) -> &'tcx Result<(
+        LocalDefIdSet,
+        LocalDefIdSet,
         LocalDefIdSet,
         LocalDefIdMap<FxIndexSet<DefId>>,
     ), ErrorGuaranteed> {