Extend the predicates with unstable feature attribute

Author: tiif

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -9,7 +9,7 @@ use rustc_middle::ty::{
     self, GenericPredicates, ImplTraitInTraitData, Ty, TyCtxt, TypeVisitable, TypeVisitor, Upcast,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_span::{DUMMY_SP, Ident, Span};
+use rustc_span::{DUMMY_SP, Ident, Span, sym};
 use tracing::{debug, instrument, trace};
 
 use super::item_bounds::explicit_item_bounds_with_filter;
@@ -69,6 +69,7 @@ pub(super) fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredic
         );
     }
 
+
     debug!("predicates_of({:?}) = {:?}", def_id, result);
     result
 }
@@ -318,6 +319,18 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
         predicates.extend(const_evaluatable_predicates_of(tcx, def_id, &predicates));
     }
 
+    for attr in tcx.get_attrs(def_id, sym::allow_unstable_feature) {
+        if let Some(list) = attr.meta_item_list() {
+            for item in list.iter() {
+                // TODO: deal with error later
+                let feature_name = item.name().unwrap();
+                predicates
+                    .insert((ty::ClauseKind::UnstableFeature(feature_name).upcast(tcx), tcx.def_span(def_id)));
+
+            }
+        }
+    }
+
     let mut predicates: Vec<_> = predicates.into_iter().collect();
 
     // Subtle: before we store the predicates into the tcx, we