Add feature and attribute definition

compiler/rustc_feature/src/active.rs

@@ -391,6 +391,8 @@ declare_features! (
     (active, doc_masked, "1.21.0", Some(44027), None),
     /// Allows `dyn* Trait` objects.
     (incomplete, dyn_star, "1.65.0", Some(102425), None),
+    // Uses generic effect parameters for ~const bounds
+    (active, effects, "CURRENT_RUSTC_VERSION", Some(102090), None),
     /// Allows `X..Y` patterns.
     (active, exclusive_range_pattern, "1.11.0", Some(37854), None),
     /// Allows exhaustive pattern matching on types that contain uninhabited types.

compiler/rustc_feature/src/builtin_attrs.rs

@@ -723,6 +723,12 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         and it is only intended to be used in `alloc`."
     ),
 
+    rustc_attr!(
+        rustc_host, AttributeType::Normal, template!(Word), ErrorFollowing,
+        "#[rustc_host] annotates const generic parameters as the `host` effect param, \
+        and it is only intended for internal use and as a desugaring."
+    ),
+
     BuiltinAttribute {
         name: sym::rustc_diagnostic_item,
         // FIXME: This can be `true` once we always use `tcx.is_diagnostic_item`.

compiler/rustc_span/src/symbol.rs

@@ -656,6 +656,7 @@ symbols! {
         dyn_trait,
         e,
         edition_panic,
+        effects,
         eh_catch_typeinfo,
         eh_personality,
         emit,
@@ -793,6 +794,7 @@ symbols! {
         hexagon_target_feature,
         hidden,
         homogeneous_aggregate,
+        host,
         html_favicon_url,
         html_logo_url,
         html_no_source,
@@ -1284,6 +1286,7 @@ symbols! {
         rustc_evaluate_where_clauses,
         rustc_expected_cgu_reuse,
         rustc_has_incoherent_inherent_impls,
+        rustc_host,
         rustc_if_this_changed,
         rustc_inherit_overflow_checks,
         rustc_insignificant_dtor,