adds feature gating of no_coverage at either crate- or function-level

compiler/rustc_feature/src/active.rs

@@ -649,6 +649,10 @@ declare_features! (
     /// Allows `extern "wasm" fn`
     (active, wasm_abi, "1.53.0", Some(83788), None),
 
+    /// Allows function attribute `#[no_coverage]`, to bypass coverage
+    /// instrumentation of that function.
+    (active, no_coverage, "1.53.0", Some(84605), None),
+
     /// Allows trait bounds in `const fn`.
     (active, const_fn_trait_bound, "1.53.0", Some(57563), None),
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -264,7 +264,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     // Code generation:
     ungated!(inline, AssumedUsed, template!(Word, List: "always|never")),
-    ungated!(no_coverage, AssumedUsed, template!(Word)),
     ungated!(cold, AssumedUsed, template!(Word)),
     ungated!(no_builtins, AssumedUsed, template!(Word)),
     ungated!(target_feature, AssumedUsed, template!(List: r#"enable = "name""#)),
@@ -274,6 +273,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         template!(List: "address, memory, thread"),
         experimental!(no_sanitize)
     ),
+    ungated!(
+        // Not exclusively gated at the crate level (though crate-level is
+        // supported). The feature can alternatively be enabled on individual
+        // functions.
+        no_coverage, AssumedUsed,
+        template!(Word),
+    ),
 
     // FIXME: #14408 assume docs are used since rustdoc looks at them.
     ungated!(doc, AssumedUsed, template!(List: "hidden|inline|...", NameValueStr: "string")),