Added unfulfilled_lint_expectations lint for (RFC-2383)

compiler/rustc_lint_defs/src/builtin.rs

@@ -495,6 +495,39 @@
     "unrecognized lint attribute"
 }
 
+declare_lint! {
+    /// The `unfulfilled_lint_expectations` lint detects lint trigger expectations
+    /// that have not been fulfilled.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #![feature(lint_reasons)]
+    ///
+    /// #[expect(unused_variables)]
+    /// let x = 10;
+    /// println!("{}", x);
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// It was expected that the marked code would emit a lint. This expectation
+    /// has not been fulfilled.
+    ///
+    /// The `expect` attribute can be removed if this is intended behavior otherwise
+    /// it should be investigated why the expected lint is no longer issued.
+    ///
+    /// Part of RFC 2383. The progress is being tracked in [#54503]
+    ///
+    /// [#54503]: https://github.com/rust-lang/rust/issues/54503
+    pub UNFULFILLED_LINT_EXPECTATIONS,
+    Warn,
+    "unfulfilled lint expectation",
+    @feature_gate = rustc_span::sym::lint_reasons;
+}
+
 declare_lint! {
     /// The `unused_variables` lint detects variables which are not used in
     /// any way.
@@ -3007,6 +3040,7 @@
         UNUSED_CRATE_DEPENDENCIES,
         UNUSED_QUALIFICATIONS,
         UNKNOWN_LINTS,
+        UNFULFILLED_LINT_EXPECTATIONS,
         UNUSED_VARIABLES,
         UNUSED_ASSIGNMENTS,
         DEAD_CODE,